Use of tetra-azapentamethine compounds as direct dyeing agents and novel tetraazapentamethine compounds

ABSTRACT

The invention concerns the use as direct dyeing agent of at least one tetraazapentamethine compound, a dyeing composition comprising at least such a compound, as well as a method for dyeing keratinous fibers, in particular human keratinous fibers and more particularly hair, which consists in applying at least one composition comprising such a compound. The composition also concerns tetra-azapentamethine compounds of formula (I). The invention further concerns a method for bleaching such compounds, as well as bleaching keratinous fibers previously dyed therewith.

The present invention relates to the field of dyeing keratin fibers, andrelates more particularly to the use, as a direct dye, of at least onetetraazepentamethine compound, to a dye composition comprising at leastone such compound and to a process for dyeing keratin fibers in which atleast one composition comprising such a compound is applied.

The present invention also relates to novel tetraazapentamethinecompounds and to the process for preparing them.

It is known practice to dye keratin fibers, and in particular humanhair, with dye compositions containing oxidation dye precursors, whichare generally known as oxidation bases, such as ortho- orpara-phenylenediamines, ortho- or para-aminophenols and heterocycliccompounds. These oxidation bases are colorless or weakly coloredcompounds, which, when combined with oxidizing products, give rise tocolored compounds via a process of oxidative condensation.

It is also known that the shades obtained with these oxidation bases canbe varied by combining them with couplers or coloration modifiers, thelatter agents being chosen especially from aromatic meta-diamines,meta-aminophenols, meta-diphenols and certain heterocyclic compoundssuch as indole compounds.

The variety of molecules used as oxidation bases and couplers allows awide range of colors to be obtained.

This oxidation dyeing process consists in applying to keratin fibersoxidation bases or a mixture of oxidation bases and couplers with anoxidizing agent, for example aqueous hydrogen peroxide solution, leavingthe mixture to act and then rinsing the fibers. The colorationsresulting therefrom are permanent, strong and resistant to externalagents, especially light, bad weather, washing, perspiration andrubbing. This process, which is generally performed at basic pH, makesit possible simultaneously to obtain dyeing and lightening of the fiber,which is reflected in practice by the possibility of obtaining a finalcoloration that is lighter than the original color. In addition, thelightening of the fiber has the advantageous effect of giving rise to aunified color in the case of gray hair, and of bringing out the color,i.e. of making it more visible, in the case of naturally pigmented hair.

It is also known practice to dye keratin fibers by direct dyeing. Theprocess conventionally used in direct dyeing consists in applying tokeratin fibers direct dyes, which are colored and coloring moleculesthat have affinity for the fibers, leaving the dyes to act and thenrinsing the fibers.

It is known practice, for example, to use nitrobenzene, anthraquinone,nitropyridine, azo, xanthene, acridine, azine or triarylmethane directdyes.

This results in colorations that are particularly chromatic, but are,however, temporary or semipermanent on account of the nature of thebonds between the direct dyes and the keratin fiber. These interactionsare such that the dyes are easily desorbed from the surface and/or fromthe core of the fiber. The colorations generally show low dyeing powerand poor fastness with respect to washing or perspiration. These directdyes are also generally light-sensitive, since the resistance of thechromophore with respect to photochemical attack is low, which leads tofading of the coloration of the hair over time. In addition, thesensitivity of these dyes to light depends on their uniform distributionor their distribution as aggregates in and/or on the keratin fiber.

It is known practice to use direct dyes in combination with oxidizingagents. However, the direct dyes are generally sensitive to the actionof oxidizing agents such as aqueous hydrogen peroxide solution, whichgenerally makes them difficult to use in lightening direct dyecompositions based on aqueous hydrogen peroxide solution and on abasifying agent, or in oxidation dye compositions based on oxidationdyes.

Thus, it was proposed in patent applications FR-1 584 965 and JP-062 711435 to dye the hair with dye compositions based on nitro direct dyesand/or on azo dispersed dyes and ammoniacal hydrogen peroxide solution,by applying to the hair a mixture of said dyes and of said oxidizingagent, prepared just before use. However, the colorations obtained arefound to be insufficiently fast and disappear on shampooing, leaving thelightening of the hair fiber to show through. Such a coloration becomesunattractive by changing over time.

It has also been proposed in patent applications JP-53 95693 and JP-55022638 to dye the hair with compositions based on cationic direct dyesof oxazine type and ammoniacal hydrogen peroxide solution, by applyingto the hair, in first step, ammoniacal hydrogen peroxide solution, andthen, in a second step, a composition based on the oxazine direct dye.This coloration is unsatisfactory, due to the fact that it requires aprocess that is made too slow by the leave-in times of the twosuccessive steps. If, moreover, an extemporaneous mixture of the oxazinedirect dye with ammoniacal hydrogen peroxide solution is applied to thehair, no coloration, or at the very most a virtually nonexistentcoloration, of the hair fiber is obtained.

More recently, patent application FR 2 741 798 has described dyecompositions containing azo or azomethine direct dyes comprising atleast one quaternized nitrogen atom, said compositions needing to bemixed extemporaneously at basic pH with an oxidizing composition. Thesecompositions allow fast, shiny colorations with uniform glints to beobtained. However, they do not allow keratin fibers to be dyed asstrongly as with oxidation dye compositions.

Moreover, patent application FR 1 353 497, which does not howeverconcern the dyeing of keratin fibers, discloses tetraazapentamethinecompounds substituted with a benzimidazole radical and with abenzimidazolium group, which are particularly suitable for dyeing fibersbased on acrylic nitrile polymers or copolymers.

There is thus a real need for direct dyes that do not have the drawbacksof those of the prior art.

The Applicant has discovered, advantageously and unexpectedly, that itis possible to achieve this aim by using at least one monocationictetraazapentamethine compound of formula (I).

These direct dyes are chromatic and allow keratin fibers to be dyed asstrongly as with oxidation dyes, they are just as light-stable asoxidation dyes, and they are also resistant to bad weather, washing andperspiration. These direct dyes allow keratin fibers to be dyed in avery wide and in particular very chromatic range of colors, withoutforgetting the “fundamental” shades such as blacks and browns.

One subject of the present patent application is thus the use, as adirect dye in or for the manufacture of dye compositions for keratinfibers, in particular for human keratin fibers and more particularly thehair, of at least one tetraazapentamethine compound of formula (I)

in which

-   -   W₁ represents a cationic heteroaromatic radical of formula (II)        or (III):    -   W₂ represents a heteroaromatic radical of formula (IV) or (V):        in which:    -   Z₀ represents a radical CR₂, a nitrogen atom or a radical NR₂₁,    -   Z₁ represents an oxygen or sulfur atom or a radical NR₉,    -   Z₂ represents a nitrogen atom or a radical CR₁₀,    -   Z₃ represents a nitrogen atom or a radical CR₁₁,    -   Z₄ represents a nitrogen atom or a radical CR₁₂,    -   Z₅ represents a nitrogen atom or a radical CR₁₃,    -   Z₆ represents a nitrogen atom or a radical CR₁₄,    -   Z₇ represents an oxygen or sulfur atom or a radical NR₁₅,    -   Z₈ represents a nitrogen atom or a radical CR₁₆,    -   Z₉ represents a nitrogen atom or a radical CR₁₇,    -   Z₁₀ represents a nitrogen atom or a radical CR₁₈,    -   Z₁₁ represents a nitrogen atom or a radical CR₁₉,    -   Z₁₂ represents a nitrogen atom or a radical CR₂₀,    -   Z₁₃ represents a radical CR₆, a nitrogen atom or a radical NR₂₂,    -   it being understood that each of the rings of formulae (II),        (III), (IV) and (V) comprise not more than three nitrogen atoms        and that two of the three nitrogen atoms may be contiguous,    -   the bond a of the 5-membered cationic heteroaromatic radical of        formula (II) being linked to the nitrogen atom N₁ of formula        (I),    -   the bond b of the 6-membered cationic heteroaromatic radical of        formula (III) being linked to the nitrogen atom N₁ of formula        (I),    -   the double bond a′ of the 5-membered heteroaromatic radical of        formula (IV) being linked to the nitrogen atom N₂ of formula        (I),    -   the double bond b′ of the 6-membered heteroaromatic radical of        formula (V) being linked to the nitrogen atom N₂ of formula (I),    -   the bond b, linking the cationic heteroaromatic radical of        formula (III) to the nitrogen atom N₁ of formula (I), being in        an ortho or para position relative to the nitrogen atom bearing        the radical R₄ when Z₅ represents a radical CR₁₃; the bond b        being in an ortho position relative to the nitrogen atom bearing        the radical R₄ when Z₅ represents a nitrogen atom,    -   the bond b′, linking the heteroaromatic radical of formula (V)        to the nitrogen atom N₂ of formula (I), being in an ortho or        para position relative to the nitrogen atom bearing the radical        R₇ when Z₁₁ represents a radical CR₁₉; the bond b′ being in an        ortho position relative to the nitrogen atom bearing the radical        R₇ when Z₁₁ represents a nitrogen atom,    -   R₂, R₆, R₁₀ and R₁₆ represent, independently of each other, a        hydrogen atom; a linear or branched C₁-C₄ alkyl radical, which        is unsubstituted or substituted with one to three radicals        chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,        amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; a        phenyl radical, which is unsubstituted or substituted with one        or two radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄        (poly)hydroxyalkoxy, amino and C₁-C₂ (di)alkylamino radicals; a        carboxyl radical; a sulfonylamino radical,    -   R₁, R₄, R₅, R₇, R₉, R₁₅, R₂₁ and R₂₂ represent, independently of        each other, a linear or branched C₁-C₈ alkyl radical, which is        unsubstituted or substituted with one to three radicals chosen        from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino,        C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals;    -   R₀, R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄, R₁₇, R₁₈, R₁₉ and R₂₀ represent,        independently of each other, a hydrogen atom, a linear or        branched C₁-C₁₆ hydrocarbon-based chain, this chain possibly        being saturated or unsaturated with one to three unsaturations,        this chain being unsubstituted or substituted with one to three        radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄        (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl,        sulfonic, sulfonylamino and C₂-C₄ (poly)hydroxyalkylamino        radicals or a halogen atom such as chlorine, fluorine or        bromine; a phenyl radical, which is unsubstituted or substituted        with one to three radicals chosen from hydroxyl, C₁-C₂ alkoxy,        C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino,        carboxyl, sulfonic, sulfonylamino and C₂-C₄        (poly)hydroxyalkylamino radicals or a halogen atom such as        chlorine, fluorine or bromine; a heteroaryl radical chosen from        pyrazolyl, pyrrolyl, imidazolyl, thiazolyl, oxazolyl, triazolyl,        pyridyl, pyrimidinyl, triazinyl, pyrazinyl and pyridazinyl        radicals; in addition, this hydrocarbon-based chain may be        interrupted with one or two oxygen, nitrogen or sulfur atoms or        with an SO₂ radical,    -   it being understood that R₀, R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄, R₁₇,        R₁₈, R₁₉ and R₂₀ do not comprise a peroxide bond or diazo or        nitroso radicals,    -   R₂ with R₁₀, R₁₁ with R₁₂, R₆ with R₁₆, and R₁₇ with R₁₈ can        form, independently of each other, a 5- or 6-membered        carbon-based aromatic ring, which is unsubstituted or        substituted with one or two hydroxyl, amino, (di)        (C₁-C₂)alkylamino, C₁-C₂ alkoxy or C₂-C₄ (poly)hydroxyalkylamino        radicals, X is an organic or mineral anion.

For the purposes of the present patent application, the expression“branched hydrocarbon-based chain” means a branched hydrocarbon-basedchain which can also form one to five 3- to 7-membered carbon-basedrings, this chain possibly comprising one to three unsaturations, i.e.one to three double bonds and/or triple bonds.

The term “C₂-C₄ (poly)hydroxyalkoxy” means a C₂-C₄ alkoxy groupsubstituted with 1 or 2 hydroxyl groups.

For the purposes of the present invention, the expression “C₂-C₄(poly)hydroxyalkylamino” means an alkylamino group substituted with 1 or2 hydroxyl groups.

The expression according to which the hydrocarbon-based chain may beinterrupted with one or more oxygen, nitrogen or sulfur atoms or with anSO₂ radical, or according to which this chain is unsaturated, means thatthe carbon-based chain may be modified in the following manner:

For the purposes of the present patent application, an organic ormineral anion is chosen, for example, from a halide such as chloride,bromide, fluoride or iodide; a hydroxide; a sulfate; a hydrogen sulfate;a (C₁-C₆)alkyl sulfate, for instance a methyl sulfate or an ethylsulfate; an acetate; a tartrate; an oxalate; a (C₁-C₆)alkylsulfonatesuch as methyl sulfonate; an arylsulfonate, which is unsubstituted orsubstituted with a C₁-C₄ alkyl radical, for instance a 4-tolylsulfonate.

Preferably, R₀ represents a hydrogen atom; a linear or branched C₁-C₆alkyl radical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, C₂-C₄ (poly)hydroxyalkylamino, carboxyl andsulfonic radicals; a phenyl radical, which is unsubstituted orsubstituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyland sulfonic radicals or a halogen atom such as chlorine, fluorine orbromine, an optionally cationic heteroaryl radical chosen frompyrazolyl, pyrrolyl, imidazolyl, thiazolyl, oxazolyl, triazolyl,pyridyl, pyrimidinyl, triazinyl, pyrazinyl and pyridazinyl radicals.

Even more preferably, R₀ preferably represents a hydrogen atom; a linearor branched C₁-C₃ alkyl radical, which is unsubstituted or substitutedwith one or two radicals chosen from hydroxyl, C₁-C₂ alkoxy, amino,C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; a phenyl radical,which is unsubstituted or substituted with one or two radicals chosenfrom hydroxyl, amino, C₁-C₂ (di)alkylamino and C₂-C₄(poly)hydroxyalkylamino radicals, or an optionally cationic heteroarylradical chosen from pyrazolyl, pyrrolyl, imidazolyl and pyridylradicals.

According to one particularly preferred embodiment, R₀ represents ahydrogen atom; a methyl, ethyl, propyl, butyl, 2-hydroxyethyl,2-aminoethyl, 1-carboxymethyl, 2-carboxyethyl, 2-sulfonylethyl or2-methoxyethyl; a phenyl radical, which is unsubstituted or substitutedwith one or two radicals chosen from amino, C₁-C₂ (di)alkylamino andC₂-C₄ (poly)hydroxyalkylamino radicals, or an optionally cationicheteroaryl radical chosen from pyrazolyl, pyrrolyl, imidazolyl andpyridyl radicals.

R₀ represents a hydrogen atom; a methyl, ethyl or 2-methoxyethylradical; a phenyl radical, which is unsubstituted or substituted with anamino, (di)methylamino or (di)(2-hydroxyethyl)amino radical, or anoptionally cationic heteroaryl radical chosen from imidazolyl andpyridyl radicals.

R₂, R₆, R₁₀ and R₁₆ preferably represent a hydrogen atom, a phenylradical or a C₁-C₄ alkyl radical, which is unsubstituted or substitutedwith one or two radicals chosen from hydroxyl, amino, C₁-C₂(di)alkylamino and carboxyl radicals.

According to one particularly preferred embodiment, R₂, R₆, R₁₀ and R₁₆preferably represent a hydrogen atom, a methyl, phenyl or2-hydroxymethyl radical, a carboxyl or a phenyl radical.

R₁, R₄, R₅, R₇, R₉, R₁₅, R₂₁ and R₂₂ preferably represent a C₁-C₄ alkylradical, which is unsubstituted or substituted with one or two radicalschosen from hydroxyl, C₁-C₂ alkoxy, amino, C₁-C₂ (di)alkylamino,carboxyl and sulfonic radicals.

According to one particularly preferred embodiment, R₁, R₄, R₅, R₇, R₉,R₁₅, R₂₁ and R₂₂ preferably represent a methyl, ethyl, 2-hydroxyethyl,1-carboxymethyl, 2-carboxyethyl or 2-sulfonylethyl radical.

R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄, R₁₇, R₁₈, R₁₉ and R₂₀ preferably represent,independently of each other, a hydrogen atom; a linear or branched C₁-C₄alkyl radical, which is unsubstituted or substituted with one or tworadicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; a phenylradical, which is unsubstituted or substituted with one or two radicalschosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino,C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals or a halogen atomsuch as chlorine, fluorine or bromine; a sulfonylamino radical; a C₂-C₄(poly)hydroxyalkylamino radical.

More preferably, R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄, R₁₇, R₁₈, R₁₉ and R₂₀represent a hydrogen atom, a C₁-C₄ alkyl radical, which is unsubstitutedor substituted with one or two radicals chosen from hydroxyl radicals ora C₁-C₂ alkoxy radical; an amino radical; a C₁-C₂ (di)alkylaminoradical; a carboxyl radical; a C₂-C₄ (poly)hydroxyalkylamino radical.

According to one particularly preferred embodiment, R₃, R₈, R₁₁, R₁₂,R₁₃, R₁₄, R₁₇, R₁₈, R₁₉ and R₂₀ represent, independently of each other,a hydrogen atom, a methyl or 2-hydroxymethyl radical, a carboxyl, amethoxy, ethoxy or 2-hydroxyethyloxy radical, or an amino, methylamino,dimethylamino or 2-hydroxyethylamino radical.

The compounds of formula (I) preferably used are those for which, informula (I), W₁ is a 2-benzimidazolium radical and W₂ is a2-benzimidazole radical. Even more preferably, they are the followingcompounds:

-   -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-methyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-ethyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-isopropyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-phenyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-methyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-methyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride

A second subject of the present invention consists of a composition fordyeing keratin fibers, in particular human keratin fibers and moreparticularly the hair, comprising, in a medium that is suitable fordyeing, at least one compound of formula (I) as a direct dye.

Preferably, the compounds of formula (I) are present in the compositionaccording to the present invention in a weight concentration rangingfrom 0.001% to 5% and preferably from 0.05% to 2% relative to the totalweight of the composition.

According to one variant, the composition according to the presentinvention also comprises at least one direct dye other than those offormula (I) according to the invention, chosen especially from the groupformed by neutral, acidic or cationic nitrobenzene direct dyes, neutral,acidic or cationic azo direct dyes, neutral, acidic or cationic quinoneand in particular anthraquinone direct dyes, azine direct dyes, methinedirect dyes, triarylmethane direct dyes, indoamine dyes and naturaldirect dyes. The additional direct dye(s) preferably represent(s) from0.001% to 20% by weight approximately and even more preferably from0.005% to 10% by weight approximately relative to the total weight ofthe composition.

The composition of the invention may also comprise an oxidizing agent.This oxidizing agent may be any oxidizing agent used conventionally fordyeing or bleaching keratin fibers. The oxidizing agent is preferablychosen from hydrogen peroxide, urea peroxide, alkali metal bromates,persalts such as perborates and persulfates, peracids and enzymes, amongwhich mention may be made of 2-electron oxidoreductases such asuricases, peroxidases and 4-electron oxidoreductases, for instancelaccases. It is particularly preferred to use hydrogen peroxide asoxidizing agent.

The composition according to the invention may also comprise anoxidation base. This oxidation base may be chosen from the oxidationbases conventionally used in oxidation dyeing, for examplepara-phenylenediamines, bis(phenyl)alkylenediamines, para-aminophenols,ortho-aminophenols and heterocyclic bases.

The composition according to the invention may also contain one or morecouplers conventionally used for dyeing keratin fibers. Among thesecouplers, mention may be made especially of meta-phenylenediamines,meta-aminophenols, meta-diphenols, naphthalene-based couplers andheterocyclic couplers.

In the composition of the present invention, the coupler(s) is (are)generally present in an amount ranging from 0.001% to 10% by weightapproximately and more preferably from 0.005% to 6% relative to thetotal weight of the dye composition. The oxidation base(s) is (are)present in an amount preferably ranging from 0.001% to 10% by weightapproximately and more preferably from 0.005% to 6% by weightapproximately relative to the total weight of the dye composition.

In general, the addition salts with an acid that may be used in thecontext of the dye compositions of the invention for the oxidation basesand couplers are chosen especially from the hydrochlorides,hydrobromides, sulfates, citrates, succinates, tartrates, lactates,tosylates, benzenesulfonates, phosphates and acetates.

The medium that is suitable for dyeing, also known as the dye support,generally consists of water or of a mixture of water and of at least oneorganic solvent to dissolve the compounds that would not be sufficientlywater-soluble. Examples of organic solvents that may be mentionedinclude C₁-C₄ lower alkanols such as ethanol and isopropanol, polyolsand polyol ethers, for instance 2-butoxyethanol, propylene glycol,propylene glycol monomethyl ether, diethylene glycol monoethyl ether andmonomethyl ether, and also aromatic alcohols, for instance benzylalcohol or phenoxyethanol, and mixtures thereof.

The organic solvents may be present in proportions preferably of between1% and 40% by weight approximately and even more preferably between 5%and 30% by weight approximately relative to the total weight of the dyecomposition.

The dye composition in accordance with the invention may also containvarious adjuvants conventionally used in compositions for dyeing thehair, such as anionic, cationic, nonionic, amphoteric or zwitterionicsurfactants or mixtures thereof, anionic, cationic, nonionic, amphotericor zwitterionic polymers or mixtures thereof, mineral or organicthickeners, and in particular anionic, cationic, nonionic and amphotericassociative polymers, antioxidants, penetrating agents, sequesteringagents, fragrances, buffers, dispersants, conditioning agents, forinstance volatile or nonvolatile, modified or unmodified silicones,film-forming agents, ceramides, preserving agents and opacifiers.

The adjuvants mentioned above are generally present in an amount foreach of between 0.01% and 20% by weight relative to the weight of thecomposition.

Needless to say, a person skilled in the art will take care to selectthis or these optional additional compound(s) such that the advantageousproperties intrinsically associated with the dye composition inaccordance with the invention are not, or are not substantially,adversely affected by the envisaged addition(s).

The pH of the dye composition in accordance with the invention isgenerally between 3 and 12 approximately and preferably between 5 and 11approximately. It may be adjusted to the desired value by means ofacidifying or basifying agents usually used in the dyeing of keratinfibers, or alternatively using standard buffer systems.

Among the acidifying agents that may be mentioned, for example, aremineral or organic acids, for instance hydrochloric acid,orthophosphoric acid, sulfuric acid, carboxylic acids, for instanceacetic acid, tartaric acid, citric acid and lactic acid, and sulfonicacids.

Among the basifying agents that may be mentioned, for example, areaqueous ammonia, alkali metal carbonates, alkanolamines such asmonoethanolamine, diethanolamine and triethanolamine and derivativesthereof, sodium hydroxide, potassium hydroxide and the compounds offormula (III) below:

in which W is a propylene residue optionally substituted with a hydroxylgroup or a C₁-C₄ alkyl radical, R_(a), R_(b), R_(c) and R_(d), which maybe identical or different, represent a hydrogen atom or a C₁-C₄ alkyl orC₁-C₄ hydroxyalkyl radical.

The dye composition according to the invention may be in various forms,such as in the form of liquids, creams or gels or in any other form thatis suitable for dyeing keratin fibers and especially human hair.

A third subject of the present invention consists of a direct dyeingprocess, which comprises the application of a dye composition comprisingat least one dye of formula (I) as defined above to keratin fibers, inparticular human keratin fibers and more particularly the hair, for atime that is sufficient to develop the desired coloration. The fibersare then rinsed and then dried.

The composition containing the dye of formula (I) may be applied to thekeratin fibers in the presence of an oxidizing agent, which brings aboutthe bleaching of the fiber (lightening direct dyeing process). Thisoxidizing agent may be added to the composition containing the dye offormula (I) at the time of use or directly onto the keratin fiber.

A subject of the invention is also an oxidation-dyeing process, whichcomprises the application to the fibers of a dye composition comprisingat least one dye of formula (I), at least one oxidation base andoptionally at least one coupler, in the presence of an oxidizing agent.

The oxidation base, the coupler and the oxidizing agent are as definedabove.

The color may be revealed at acid, neutral or alkaline pH and theoxidizing agent may be added to the composition according to theinvention just at the time of use, or it may be used starting with anoxidizing composition containing it, in which case it is applied to thefibers simultaneously with or sequentially to the dye composition.

In the case of the lightening direct dyeing or oxidation dyeing, the dyecomposition is mixed, preferably at the time of use, with a compositioncontaining, in a medium that is suitable for dyeing, at least oneoxidizing agent, this oxidizing agent being present in an amount that issufficient to develop a coloration. The mixture obtained is then appliedto the keratin fibers. After a leave-in time of 3 to 50 minutesapproximately and preferably 5 to 30 minutes approximately, the keratinfibers are rinsed, washed with shampoo, rinsed again and then dried.

The oxidizing composition may also contain various adjuvantsconventionally used in compositions for dyeing the hair, and as definedabove.

The pH of the oxidizing composition containing the oxidizing agent issuch that, after mixing with the dye composition, the pH of theresulting composition applied to the keratin fibers preferably rangesbetween 3 and 12 approximately and even more preferably between 5 and11. It may be adjusted to the desired value using acidifying orbasifying agents usually used in the dyeing of keratin fibers, and asdefined above.

The composition that is finally applied to the keratin fibers may be invarious forms, such as in the form of liquids, creams or gels or in anyother form that is suitable for dyeing keratin fibers, and especiallyhuman hair.

A subject of the present invention is, furthermore, a process ofbleaching of the direct dyes, which form the subject of the inventionand which have just been described. Advantageously, this bleachingprocess may be applied to keratin fibers that have been dyed beforehandin accordance with the dyeing processes that have just been described.One of the advantages of this process is that the natural color of thefibers before dyeing with the composition according to the invention isconserved, and only the color provided by the direct dye is removed.

This process also has the advantage of being quick and easy to perform.Thus, the process consists in applying to the compound of formulae (I)and (I′) a bleaching composition comprising at least one reducing agentchosen from reducing agents comprising sulfur. When the process isapplied to keratin fibers, it consists in performing the followingsteps:

-   -   a) a bleaching composition comprising, in a suitable medium, at        least one reducing agent chosen from reducing agents comprising        sulfur is applied to the fibers which have been treated        beforehand with a dye composition according to the invention;    -   b) this composition is left to act for a time that is sufficient        for the bleaching to take place;    -   c) the fibers are optionally rinsed;    -   d) the fibers are washed, rinsed and then dried.

By way of example, the reducing agents comprising sulfur are chosen fromcompounds containing at least one thiol, sulfide or sulfite function.

Among the thiols that may be used as reducing compounds, mention may bemade of thioglycolic acid, thiolactic acid, the alkali metal oralkaline-earth metal salts thereof (for instance the sodium, potassiumor calcium salts) and esters thereof; β-mercaptoethanol, cysteine,cysteamine and derivatives thereof; homocysteine and a salt thereof;mercaptoaldehydes; penicillamine; glutathione. These compounds may beused alone or as mixtures.

As regards the sulfites that may be used as reducing agents, among whichare also featured bisulfites and hydrosulfites, the alkali metal,alkaline-earth metal or ammonium salts, and also mixtures thereof, aresuitable. Mention may be made more particularly of sodium sulfite,sodium metasulfite and sodium hydrosulfite.

As regards the sulfides, among which are also featured disulfides,mention may be made especially of cystine.

The content of reducing agent in the composition is advantageouslybetween 0.01% and 10% by weight of the dye-bleaching composition andpreferably between 0.1% and 5% by weight of the said bleachingcomposition.

The medium of the composition conventionally comprises water or anorganic solvent. Everything that has been stated hereinabove regardingthe medium of the dye composition remains valid, and reference may bemade thereto.

The composition may similarly comprise conventional adjuvants such asanionic, cationic, nonionic, amphoteric or zwitterionic surfactants ormixtures thereof, anionic, cationic, nonionic, amphoteric orzwitterionic polymers or mixtures thereof, mineral or organicthickeners, and in particular anionic, cationic, nonionic and amphotericassociative polymers, antioxidants, penetrating agents, sequesteringagents, fragrances, buffers, dispersants, conditioning agents, forinstance volatile or nonvolatile, modified or unmodified silicones,film-forming agents, ceramides, preserving agents and opacifiers.

The adjuvants mentioned above are generally present in an amount foreach of between 0.01% and 20% by weight relative to the weight of thebleaching composition. Needless to say, a person skilled in the art willtake care to select this or these optional adjuvant(s) such that theadvantageous properties intrinsically associated with the use of thebleaching composition are not, or are not substantially, adverselyaffected by the envisaged addition(s).

The pH of the bleaching composition is generally between 6 and 10 andadvantageously between 7 and 9. It may be adjusted to the desired valueby means of acidifying or basifying agents usually used in the field,lists of which have been given hereinabove, or alternatively usingstandard buffer systems.

The bleaching composition may be applied to either dry hair or wet hair.

As a guide, the temperature at which the bleaching process is performedis between 15 and 50° C. and preferably in the region of roomtemperature.

The leave-in time for the composition is generally between 1 and 30minutes and more particularly between 2 and 20 minutes. It should benoted that this range is given merely as a guide. Specifically, it maybe determined without difficulty by a person skilled in the art, thebleaching of the hair being able to be observed visually, since thephenomenon is visible. Generally, the larger the content of reducingagent and/or the higher the temperature, the shorter the leave-in timeto bleach the dye or the hair that has been dyed beforehand with thedyes according to the invention.

The present invention also relates to the tetraazepentamethine compoundsof formula (I′)

in which

-   -   W′₁ represents a cationic heteroaromatic radical of formula        (II′) or (III′)    -   W′₂ represents a heteroaromatic radical of formula (IV′) or        (V′):        in which:    -   Z′₀ represents a radical CR′₂, a nitrogen atom or a radical        NR′₂₁,    -   Z′₁ represents an oxygen atom or a radical NR′₉,    -   Z′₂ represents a nitrogen atom or a radical CR′₁₀,    -   Z′₃ represents a nitrogen atom or a radical CR′₁₁,    -   Z′₄ represents a nitrogen atom or a radical CR′₁₂,    -   Z′₅ represents a nitrogen atom or a radical CR′₁₃,    -   Z′₆ represents a nitrogen atom or a radical CR′₁₄,    -   Z′₇ represents an oxygen atom or a radical NR′₁₅,    -   Z′₈ represents a nitrogen atom or a radical CR′₁₆,    -   Z′₉ represents a nitrogen atom or a radical CR′₁₇,    -   Z′₁₀ represents a nitrogen atom or a radical CR′₁₈,    -   Z′₁₁ represents a nitrogen atom or a radical CR′₁₉,    -   Z′₁₂ represents a nitrogen atom or a radical CR′₂₀,    -   Z′₁₃ represents a radical CR′₆, a nitrogen atom or a radical        NR′₂₂,    -   it being understood that each of the rings of formulae (II′),        (III′), (IV′) and (V′) comprise not more than three nitrogen        atoms and that two of the three nitrogen atoms may be        contiguous,    -   the bond a of the 5-membered cationic heteroaromatic radical of        formula (II′) being linked to the nitrogen atom N₁ of formula        (I′),    -   the bond b of the 6-membered cationic heteroaromatic radical of        formula (III′) being linked to the nitrogen atom N₁ of formula        (I′),    -   the double bond a′ of the 5-membered heteroaromatic radical of        formula (IV′) being linked to the nitrogen atom N₂ of formula        (I′),    -   the double bond b′ of the 6-membered heteroaromatic radical of        formula (V′) being linked to the nitrogen atom N₂ of formula        (I′),    -   the bond b, linking the cationic heteroaromatic radical of        formula (III′) to the nitrogen atom N₁ of formula (I′), being in        an ortho or para position relative to the nitrogen atom bearing        the radical R′₄ when Z′₅ represents a radical CR′₁₃; the bond b        being in an ortho position relative to the nitrogen atom bearing        the radical R′₄ when Z′₅ represents a nitrogen atom,    -   the bond b′, linking the heteroaromatic radical of formula (V′)        to the nitrogen atom N₂ of formula (I′), being in an ortho or        para position relative to the nitrogen atom bearing the radical        R′₇ when Z′₁₁ represents a radical CR′₁₉; the bond b′ being in        an ortho position relative to the nitrogen atom bearing the        radical R′₇ when Z′₁₁ represents a nitrogen atom,    -   R′₂, R′₆, R′₁₀ and R′₁₆ represent, independently of each other,        a hydrogen atom; a linear or branched C₁-C₄ alkyl radical, which        is unsubstituted or substituted with one to three radicals        chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,        amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; a        phenyl radical, which is unsubstituted or substituted with one        or two radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄        (poly)hydroxyalkoxy, amino and C₁-C₂ (di)alkylamino radicals; a        carboxyl radical; a sulfonylamino radical,    -   R′₁, R′₄, R′₅, R′₇, R′₉, R′₁₅, R′₂₁ and R′₂₂ represent,        independently of each other, a linear or branched C₁-C₈ alkyl        radical, which is unsubstituted or substituted with one to three        radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄        (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl and        sulfonic radicals;    -   R′₀, R′₃, R′₈, R′₁₁, R′₁₂, R′₁₃, R′₁₄, R′₁₇, R′₁₈, R′₁₉ and R′₂₀        represent, independently of each other, a hydrogen atom, a        linear or branched C₁-C₁₆ hydrocarbon-based chain, this chain        possibly being saturated or unsaturated with one to three        unsaturations, this chain being unsubstituted or substituted        with one to three radicals chosen from hydroxyl, C₁-C₂ alkoxy,        C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino,        carboxyl, sulfonic, sulfonylamino and C₂-C₄        (poly)hydroxyalkylamino radicals or a halogen atom such as        chlorine, fluorine or bromine; a phenyl radical, which is        unsubstituted or substituted with one to three radicals chosen        from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino,        C₁-C₂ (di)alkylamino, carboxyl, sulfonic, sulfonylamino and        C₂-C₄ (poly)hydroxyalkylamino radicals or a halogen atom such as        chlorine, fluorine or bromine; a heteroaryl radical chosen from        pyrazolyl, pyrrolyl, imidazolyl, thiazolyl, oxazolyl, triazolyl,        pyridyl, pyrimidinyl, triazinyl, pyrazinyl and pyridazinyl        radicals; in addition, this hydrocarbon-based chain may be        interrupted with one or two oxygen, nitrogen or sulfur atoms or        with an SO₂ radical,    -   R′₂ with R′₁₀, R′₁₁, with R′₁₂, R′₆ with R′₁₆, and R′₁₇ with        R′₁₈ being able to form, independently of each other, a 5- or        6-membered carbon-based aromatic ring, which is unsubstituted or        substituted with one or two hydroxyl, amino, (di)        (C₁-C₂)alkylamino, C₁-C₂ alkoxy or C₂-C₄ (poly)hydroxyalkylamino        radicals, subject to W′₁ and W′₂ not representing,        simultaneously, the same bicyclic system, it being understood        that R′₀, R′₃, R′₈, R′₁₁, R′₁₂, R′₁₃, R′₁₄, R′₁₇, R′₁₈, R′₁₉ and        R′₂₀ do not comprise a peroxide bond or diazo or nitroso        radicals,    -   X is an organic or mineral anion.

Preferably, R′₀ represents a hydrogen atom; a linear or branched C₁-C₆alkyl radical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, C₂-C₄ (poly)hydroxyalkylamino, carboxyl andsulfonic radicals; a phenyl radical, which is unsubstituted orsubstituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyland sulfonic radicals or a halogen atom such as chlorine, fluorine orbromine; an optionally cationic heteroaryl radical chosen frompyrazolyl, pyrrolyl, imidazolyl, thiazolyl, oxazolyl, triazolyl,pyridyl, pyrimidinyl, triazinyl, pyrazinyl and pyridazinyl radicals.

Even more preferably, R′₀ preferably represents a hydrogen atom; alinear or branched C₁-C₃ alkyl radical, which is unsubstituted orsubstituted with one or two radicals chosen from hydroxyl, C₁-C₂ alkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; a phenylradical, which is unsubstituted or substituted with one or two radicalschosen from hydroxyl, amino, C₁-C₂ (di)alkylamino and C₂-C₄(poly)hydroxyalkylamino radicals, or an optionally cationic heteroarylradical chosen from pyrazolyl, pyrrolyl, imidazolyl and pyridylradicals.

According to one particularly preferred embodiment, R′₀ represents ahydrogen atom; a methyl, ethyl, propyl, butyl, 2-hydroxyethyl,2-aminoethyl, 1-carboxymethyl, 2-carboxyethyl, 2-sulfonylethyl or2-methoxyethyl; a phenyl radical, which is unsubstituted or substitutedwith one or two radicals chosen from amino, C₁-C₂ (di)alkylamino andC₂-C₄ (poly)hydroxyalkylamino radicals, or an optionally cationicheteroaryl radical chosen from pyrazolyl, pyrrolyl, imidazolyl andpyridyl radicals.

R′₀ represents a hydrogen atom; a methyl, ethyl or 2-methoxyethylradical; a phenyl radical, which is unsubstituted or substituted with anamino, (di)methylamino or (di)(2-hydroxyethyl)amino radical, or anoptionally cationic heteroaryl radical chosen from pyrazolyl, pyrrolyl,imidazolyl and pyridyl radicals.

R′₂, R′₆, R′₁₀ and R′₁₆ preferably represent a hydrogen atom, a C₁-C₄alkyl radical, which is unsubstituted or substituted with one or tworadicals chosen from hydroxyl, amino, C₁-C₂ (di)alkylamino and carboxylradicals, or a phenyl radical.

According to one particularly preferred embodiment, R′₂, R′₆, R′₁₀ andR′₁₆ preferably represent a hydrogen atom, a methyl, phenyl or2-hydroxymethyl radical or a carboxyl.

R′₁, R′₄, R′₅, R′₇, R′₉, R′₁₅, R′₂₁ and R′₂₂ preferably represent aC₁-C₄ alkyl radical, which is unsubstituted or substituted with one ortwo radicals chosen from hydroxyl, C₁-C₂ alkoxy, amino, C₁-C₂(di)alkylamino, carboxyl and sulfonic radicals.

According to one particularly preferred embodiment, R′₁, R′₄, R′₅, R′₇,R′₉, R′₁₅, R′₂₁ and R′₂₂ preferably represent a methyl, ethyl,2-hydroxyethyl, 1-carboxymethyl, 2-carboxyethyl or 2-sulfonylethylradical. R′₃, R′₈, R′₁₁, R′₁₂, R′₁₃, R′₁₄, R′₁₇, R′₁₈, R′₁₉ and R′₂₀preferably represent, independently of each other, a hydrogen atom; alinear or branched C₁-C₄ alkyl radical, which is unsubstituted orsubstituted with one or two radicals chosen from hydroxyl, C₁-C₂ alkoxy,C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl andsulfonic radicals; a phenyl radical, which is unsubstituted orsubstituted with one or two radicals chosen from hydroxyl, C₁-C₂ alkoxy,C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl andsulfonic radicals or a halogen atom such as chlorine, fluorine orbromine; a sulfonylamino radical; a C₂-C₄ (poly)hydroxyalkylaminoradical.

More preferably, R′₃, R′₈, R′₁₁, R′₁₂, R′₁₃, R′₁₄, R′₁₇, R′₁₈, R′₁₉ andR′₂₀ represent a hydrogen atom, a C₁-C₄ alkyl radical, which isunsubstituted or substituted with one or two radicals chosen fromhydroxyl radicals or a C₁-C₂ alkoxy radical; an amino radical; a C₁-C₂(di)alkylamino radical; a carboxyl radical; a C₂-C₄(poly)hydroxyalkylamino radical.

According to one particularly preferred embodiment, R′₃, R′₈, R′₁₁,R′₁₂, R′₁₃, R′₁₄, R′₁₇, R′₁₈, R′₁₉ and R′₂₀ represent, independently ofeach other, a hydrogen atom, a methyl or 2-hydroxymethyl radical, acarboxyl, a methoxy, ethoxy or 2-hydroxyethyloxy radical, or an amino,methylamino, dimethylamino or 2-hydroxyethylamino radical.

A. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 2-pyridinium radical and W′₂is a 2-pyridine radical. Even more preferably, they are the followingcompounds:

-   -   2-[5-(N-methyl-2-pyridinylidene)-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-4-pyrrolidino-N-methylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(2-pyridinyl)-1-formazano]-N-hydroxyethylpyridinium        bromide    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(2-N-methylpyridinylium        methosulfate)-1-formazano]-N-hydroxyethylpyridinium bromide    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-1-formazano]-N-carboxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-carboxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-carboxyethylpyridinium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-carboxyethylpyridinium        chloride

B. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 4-pyridinium radical and W′₂is a 4-pyridine radical. Even more preferably, they are the followingcompounds:

-   -   4-[5-(N-methyl-4-pyridinylidene)-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-methyl-4-pyridinylidene)-3-methyl-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-methyl-4-pyridinylidene)-3-ethyl-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-methyl-4-pyridinylidene)-3-isopropyl-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-methyl-4-pyridinylidene)-3-phenyl-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-methyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-methyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-methyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-methylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-hydroxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-1-formazano]-N-carboxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-N-carboxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-carboxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-carboxyethylpyridinium        chloride    -   4-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-carboxyethylpyridinium        chloride

C. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 2-imidazolium radical andW′₂ is a 2-imidazole radical. Even more preferably, they are thefollowing compounds:

-   -   2-[5-(1,3-dimethyl-2-imidazolidene)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-imidazolidene)-3-methyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-imidazolidene)-3-ethyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-imidazolidene)-3-isopropyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-imidazolidene)-3-phenyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-imidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-imidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dimethyl-2-imidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-methyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-methyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride

D. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 5-pyrazolium radical and W′₂is a 5-pyrazole radical. Even more preferably, they are the followingcompounds:

-   -   5-[5-(1,2-dimethyl-5-pyrazolidene)-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dimethyl-5-pyrazolidene)-3-methyl-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dimethyl-5-pyrazolidene)-3-ethyl-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dimethyl-5-pyrazolidene)-3-isopropyl-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dimethyl-5-pyrazolidene)-3-phenyl-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dimethyl-5-pyrazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dimethyl-5-pyrazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dimethyl-5-pyrazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,2-dimethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-methyl-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-ethyl-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-phenyl-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-isopropyl-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,2-dihydroxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-methyl-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-ethyl-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-phenyl-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-isopropyl-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride    -   5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,2-dicarboxyethylpyrazolinium        chloride

E. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 2-benzimidazolium radicaland W′₂ is a 2-pyridine radical. Even more preferably, they are thefollowing compounds:

-   -   2-[5-(N-methyl-2-pyridinylidene)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride

F. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 2-benzimidazolium radicaland W′₂ is a 4-pyridine radical. Even more preferably, they are thefollowing compounds:

-   -   2-[5-(N-methyl-4-pyridinylidene)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-(5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazolium        chloride

G. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 2-imidazolium radical andW′₂ is a 2-pyridine radical. Even more preferably, they are thefollowing compounds:

-   -   2-[5-(N-methyl-2-pyridinylidene)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride

H. Preferably, the compounds of formula (I′) are chosen from the familydefined by the compounds for which W′₁ is a 2-imidazolium radical andW′₂ is a 4-pyridine radical. Even more preferably, they are thefollowing compounds:

-   -   2-[5-(N-methyl-4-pyridinylidene)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-methyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride    -   2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylimidazolium        chloride

The novel compounds and novel families of compounds given in the abovelists may be used as direct dyes in the dye compositions according tothe invention.

The present invention also relates to a process for preparing thecompound of formula (I′), in which at least two equivalents of at leastone hydrazone chosen from the hydrazones of formula A and the hydrazonesof formula B:

in which Z₁₄, Z₁₅, Z₁₆ and R₂₅ have the same meanings as Z′₇, Z′₈, Z′₁₃,and R′₅, respectively, of formula (IV)′,

-   -   Y being an organic or mineral anion,    -   x being an integer ranging from 1 to 3,    -   Z₁₇, Z₁₈, Z₁₉, Z₂₀, R₂₆ and R₂₇ have the same meanings as Z′₉,        Z′₁₀, Z′₁₁, Z′₁₂, R′₈ and R′₇, respectively, of formula (V′),    -   Y′ being an organic or mineral anion,    -   x′ being an integer ranging from 1 to 3, are reacted with one        equivalent of an aldehyde of formula R₂₃CHO, R₂₃ having the same        meaning as R′₀ of formula (I′). Two equivalents of the same        hydrazone or of two different hydrazones may thus be reacted.

According to one preferred variant, the aldehyde of formula R₂₃CHO isgenerated in the reaction medium from an aldehyde precursor of formulaR′₂₃CH₂OH in the presence of an oxidizing system; R′₂₃ then has the samemeaning as R′₀ of formula (I′).

This oxidizing system may be a chemical oxidizing agent or abiocatalytic oxidizing agent such as an enzyme.

In particular, the process for preparing the compound of formula (I′)according to the present invention, and the process for preparing thecompound of formula (I), may be performed in the presence of an aldehydeprecursor of formula R′₂₃CH₂OH and of at least one enzyme capable ofgenerating an aldehyde from the aldehyde precursor of formula R′₂₃CH₂OH.

The process for enzymatically synthesizing the compounds of formula (I)defined above is performed by reacting at least two equivalents of atleast one hydrazone chosen from the hydrazones of formula A and thehydrazones of formula B in which Z₁₄, Z₁₅, Z₁₆ and R₂₅ have the samemeanings as Z₇, Z₈, Z₁₃ and R₅, respectively, of formula (IV),

-   -   Y being an organic or mineral anion,    -   x being an integer ranging from 1 to 3,    -   Z₁₇, Z₁₈, Z₁₉, Z₂₀, R₂₆ and R₂₇ having the same meanings as Z₉,        Z₁₀, Z₁₁, Z₁₂, R₈ and R₇, respectively, of formula (V),    -   Y′ being an organic or mineral anion,    -   x′ being an integer ranging from 1 to 3, with one equivalent of        an aldehyde of formula R₂₃CHO, R₂₃ having the same meaning as R₀        of formula (I).

A subject of the present invention is also such a process.

Depending on the reagents used, the reaction is performed with orwithout an oxidizing system, with or without a cofactor for the enzyme,and with or without a system for regenerating the cofactor.

For the purpose of the present patent application, the term “without anoxidizing system” means that no oxidizing system other than atmosphericoxygen is used.

Preferably, the reaction is performed in aerobic medium at a pH ofbetween 3 and 11 and at a temperature of between 6° C. and 80° C.

More generally, the aldehyde precursor that may be used to prepare thecompound of formula (I′) or the compound of formula (I) may be chosenfrom primary alcohols, sarcosine, 4-hydroxymandelate, N6-methyllysine,dimethylglycine, methylglutamate, 2-oxo acids, for example 2-oxo acidpyruvate, benzoylformate, phenylpyruvate or threonine. It willpreferably be chosen from primary alcohols.

The enzymes capable of generating an aldehyde from this aldehydeprecursor may be chosen especially from the alcohol dehydrogenases EC1.1.1.1, the alcohol dehydrogenases EC 1.1.1.2, the alcoholdehydrogenases EC 1.1.1.71, the aromatic alcohol dehydrogenases EC1.1.1.90, also known as aryl alcohol dehydrogenases, the aromaticalcohol dehydrogenases EC 1.1.1.97, the 3-hydroxybenzyl alcoholdehydrogenases EC 1.1.1.97, the coniferyl alcohol dehydrogenases EC1.1.1.194, the cinnamyl alcohol dehydrogenases EC 1.1.1.195, themethanol dehydrogenases EC 1.1.1.244, the aromatic alcohol oxidases EC1.1.3.7, also known as aryl alcohol oxidases, the alcohol oxidases EC1.1.3.13, the 4-hydroxymandelate oxidases EC 1.1.3.19, the long-chainhydrocarbon alcohol oxidases EC 1.1.3.20, the methanol oxidases EC1.1.3.31, the alcohol dehydrogenases EC 1.1.99.20, the sarcosineoxidases EC 1.5.3.1, the N6-methyllysine oxidases EC 1.5.3.4, thedimethylglycine oxidases EC 1.5.3.10, the sarcosine dehydrogenases EC1.5.99.1, the dimethylglycine dehydrogenases EC 1.5.99.2, themethylglutamate dehydrogenases EC 1.5.99.5, the 2-oxo aciddecarboxylases EC 4.1.1.1, the benzoylformate decarboxylases EC 4.1.1.7,the phenylpyruvate decarboxylases EC 4.1.1.43 and the threoninealdolases EC 4.1.2.5.

Mention may also be made of the following enzymes capable of generatingan aldehyde, the preferred substrate of which is given in parentheses:N-methyl L-amino acid oxidase EC 1.5.3.2 (N-methyl-L-amino acid),trimethylamine dehydrogenase EC 1.5.99.7 (trimethylamine), dimethylaminedehydrogenase EC 1.5.99.10 (dimethylamine), nitroethane oxidase EC1.7.3.1 (nitroethane), indole 2,3-dioxigenase EC 1.13.11.17 (indole),taurine dioxigenase EC 1.14.11.17 (taurine), acetoin ribose 5 phosphatetransaldolase EC 2.2.1.4 (3-hydroxybutan-2-one), diamineaminotransferase EC 2.6.1.29 (alpha omega diamine+2-oxogluterate),alkenylglycerophosphocholine hydrolase EC 3.3.2.2(alkenylglycerophosphocholine), alkenylglycerophosphoethanolaminehydrolase EC 3.3.2.5 (alkenylglycerophosphocholine), alkylalidase EC3.8.1.1 (halomethane), phosphonoacetaldehyde hydrolase EC 3.11.1.1(phosphonoacetaldehyde), indolepyruvate decarboxylase EC 4.1.1.74(3-indol-3-yl pyruvate) mandelonitrile lyase EC 4.1.2.10(mandelonitrile), hydroxymandelonitrile lyase EC 4.1.2.11(hydroxymandelonitrile), ketopantoaldolase EC 4.1.2.12(2-hydroxy-2-isopropylbutanedioate), dimethylaniline-N-oxide aldolase EC4.1.2.24 (dimethylaniline-N-oxide), phenylserine aldolase EC 4.1.2.26(phenylserine), sphinganine-1-phosphate aldolase EC 4.1.2.27(sphinganine-1-phosphate), 17-alpha hydroxyprogesterone aldolase EC4.1.2.30 (17-alpha hydroxyprogesterone), trimethylamine oxide aldolaseEC 4.1.2.23 (trimethylamine oxide), fucosterol epoxide lyase EC 4.1.2.23(fucosterol epoxide), (3E)-4-(2-carboxyphenyl)-2-oxobut-3-enoatealdolase EC 4.1.2.34 ((3E)-4-(2-carboxyphenyl)-2-oxobut-3-enoate),lactate aldolase EC 4.1.2.36 (lactate), benzoin aldolase EC 4.1.2.38(benzoin), octoamine dehydratase EC 4.2.1.87(1-(4-hydroxyphenyl)-2-aminoethanol), synephrine dehydratase EC 4.2.1.88(1-(4-hydroxyphenyl)-2-(methylamino)ethanol), ethanolamine phosphatephospholyase EC 4.2.3.2 (ethanolamine phosphate), ethanolamine ammonialyase EC 4.3.1.7 (ethanolamine), dichloromethane dehalogenase EC 4.5.1.3(dichloromethane), styrene oxide isomerase EC 5.3.99.7 (styrene oxide).

The enzyme capable of generating an aldehyde from the aldehyde precursorused in the dye composition according to the invention may be derivedfrom an extract of plants, of animals, of microorganisms (bacterium,fungus, yeast or microalga) or from viruses, or from cells that aredifferentiated or undifferentiated, obtained in vivo or in vitro, whichare genetically modified or unmodified, or synthetic (obtained viachemical or biotechnological synthesis).

Examples of useful enzymes that may be mentioned in particular are thegenera Plectranthus, Pinus, Gastropode, Manduca, Pichia, Candida,Pleurotus, and Pseudomonas, and even more particularly the followingspecies: Plectranthus colloides, Pinus strobus, which is a species ofplant origin, Gastropode mollusc and Manduca sexta, which are of animalorigin, Pichia pastoris and Candida boidinii, which are yeasts,Pleurotus pulmonarius, which is a fungus, and Pseudomonaspseudoalcaligenes, which is a bacterium.

The choice of the enzyme depends on the nature of the aldehydeprecursor. For example, when the aldehyde precursor is an alcohol, thenthe enzyme is chosen from enzymes capable of generating an aldehyde fromthis alcohol. When the aldehyde precursor is methylglutamate, then theenzyme is a methylglutamate dehydrogenase.

According to one preferred variant, the aldehyde precursor is a primaryalcohol and the enzyme is an enzyme capable of generating the aldehydefrom an alcohol. For example, when the primary alcohol is a C₁-C₆aliphatic alcohol, then the enzyme capable of generating the aldehyde ischosen from alcohol oxidases, alcohol dehydrogenases, methanoldehydrogenases and methanol oxidases. When the primary alcohol is benzylalcohol, 4-tert-butylbenzyl alcohol, 3-hydroxy-4-methoxybenzyl alcohol,veratryl alcohol, 4-methoxybenzyl alcohol, cinnamyl alcohol or2,4-hexadien-1-ol, aryl alcohol oxidases or aromatic alcoholdehydrogenases may be used as aldehyde precursor.

For the enzyme dehydrogenases, it is essential to include thecofactor(s) required for their activity, more specifically NAD⁺ or NADP⁺or other molecules capable of acting as electron acceptor. The additionof a system for regenerating the cofactors may be used for reactionpurposes or economic purposes. This regeneration system may beenzymatic, chemical or electrochemical.

A very wide variety of oxidizing agents may be used to perform thisprocess: aqueous hydrogen peroxide solution, organic peracids such asperacetic acid, persalts such as permanganate, perborate andpersulfates, chromates or bichromates, hypochlorites, hypobromites,ferricyanides, and peroxides such as manganese dioxide or lead dioxide.Aqueous hydrogen peroxide solution will preferably be used.

The concentration of enzyme substrate (aldehyde precursor) may bebetween 0.001 M and 6 M and preferably between 0.1 M and 4 M.

The reaction may be performed between pH 3 and pH 11 and preferablybetween pH 5 and pH 9.5.

The reaction temperature may be between 10° C. and 80° C. and preferablybetween 20° C. and 65° C.

The hydrazone concentration of the reaction medium is between 0.01 M and3 M and preferably between 0.1 M and 1 M.

The content of cofactor for said enzymes may be between 0.01 mM and 1 Mand preferably between 0.1 mM and 10 mM.

During the implementation of the synthesis of the compounds of formulae(I′) and (I), the reagents: the hydrazone(s), the enzyme(s), thesubstrate for said enzyme, and/or the cofactor for said enzyme, and theoxidizing agent and/or the system for regenerating the cofactor aremixed together, and the pH and the temperature are adjusted.

The present invention also relates to a process for preparing thecompound of formula (I′), in which a compound of formula (F1) or (F2)

with Z₁₄, Z₁₅, Z₁₆, R₀, R₂₄ and R₂₅ for formula F1 and Z₁₇, Z₁₈, Z₁₉,Z₂₀, R₀, R₂₄ and R₂₆ for formula F2 having the meanings described above,is reacted in the presence of one equivalent of a hydrazone of formula(A) or (B).

According to one preferred variant, the compounds of formula (F1) or(F2) may be obtained by reacting a compound of formula R″₂₃C(OR₂₄)₃ anda hydrazone of formula (A) or (B) in the presence or absence of a proticsolvent whose boiling point ranges between 66° C. and 180° C. R″₂₃ hasthe same meaning as R′₀ of formula (I′) and R₂₄ represents a radicalchosen from methyl and ethyl groups.

Preferably, the reaction is performed in the presence of triethylorthoformate and trimethyl orthoacetate at a temperature of between 0°C. and 150° C. for a period of between 30 minutes and 12 hours.

Preferably, the protic solvent is chosen from H₂O, ethanol and methanol.

EXAMPLES OF SYNTHESIS

A) Synthetic Process Using at Least One Hydrazone of Formula (A) and/or(B) and an Aldehyde Precursor of Formula R′₂₃CH₂OH

The compounds cited in formula (I′) may be synthesized by reacting atleast one hydrazone as defined in formulae (A) and (B) with one or moreenzymes such as: alcohol oxidase, alcohol dehydrogenase, oxidoreductasetransferase, and/or lyase, and the substrate(s) of formula R′₂₃CH₂OH forsaid enzyme(s) with or without oxidizing agent, with or without cofactorfor the enzyme, and with or without a system for regenerating saidcofactor. The reaction is performed at between pH 3 and pH 11 in aerobicmedium at a temperature of between 10° C. and 80° C.

Example 1

Ethanol (100%) 2 M Alcohol oxidase 1000 U (Pichia pastoris)N-hydroxyethylpyridone-2-hydrazone 0.3 M 30 mM buffer qs 100 mlKH₂PO₄/K₂HPO₄ pH 7

Example 2

Methanol (100%) 2.5 M Alcohol oxidase 2000 U (Candida boidinii)4-methoxy-N-methylpyridone-2- 0.3 M hydrazone 30 mM buffer qs 100 mlKH₂PO₄/K₂HPO₄ pH 7

Example 3

Ethanol (100%) 2 M Extract of 0.4 g Plectranthus colloides4-methoxy-N-methylpyridone-2- 0.3 M hydrazone 30 mM buffer qs 100 mlKH₂PO₄/K₂HPO₄ pH 7

Example 4

Benzyl alcohol (100%) 1 M Extract of 0.4 g Pleurotus pulmonariusN-hydroxyethylpyridone-2-hydrazone 0.3 M 30 mM buffer qs 100 mlKH₂PO₄/K₂HPO₄ pH 9

Example 5

Methanol (100%) 2.5 M Alcohol dehydrogenase 1000 U (Saccharomycescervisiae) NAD+ 10 mM N-methylpyridone-2-hydrazone 0.3 M 3% aqueoushydrogen peroxide 0.5 ml solution 30 mM buffer qs 100 ml KH₂PO₄/K₂HPO₄pH 9

Example 6

Ethanol (100%) 2.5 M Alcohol oxidase 2000 U (Pichia pastoris)1,3-dimethylimidazolidone-2- 0.3 M hydrazone 30 mM buffer qs 100 mlKH₂PO₄/K₂HPO₄ pH 8.5

Example 7

Methanol (100%) 2.5 M Alcohol oxidase 2000 U (Pichia pastoris)1,3-dimethylimidazolidone-2- 0.3 M hydrazone 30 mM buffer qs 100 mlKH₂PO₄/K₂HPO₄ pH 8.5

Example 8

Methanol (100%) 2.5 M Alcohol oxidase (Pichia pastoris) 2000 UN-methylpyridone-2-hydrazone 0.3 M N-hydroxyethylpyridone-2-hydrazone0.3 M 30 mM buffer qs 100 ml KH₂PO₄/K₂HPO₄ pH 8.5

Example 9

Ethanol 1 M Alcohol oxidase (Pichia pastoris) 50 U(2-methyl-6-methoxy-4H-pyridazin- 0.1 M 3-ylidene)hydrazine 200 mMbuffer qs 10 ml KH₂PO₄/K₂HPO₄ pH 8.5

Example 10

Ethanol 1 M Alcohol oxidase (Pichia pastoris) 50 U(2-methyl-6-pyrrolidon-1-yl-4H- 0.1 M pyridazin-3-ylidene)hydrazine 200mM buffer qs 10 ml KH₂PO₄/K₂HPO₄ pH 8.5

Example 11

The following reaction was performed: Laccase 100 U Alcohol oxidase(Pichia pastoris) 50 U N-methylpyridone-2-hydrazone 0.1 M 200 mM bufferqs 10 ml KH₂PO₄/K₂HPO₄ pH 8.5

0.1 M

A coloration appeared between 1 minute and 24 hours at room temperature.Formula of the Example Color isolated product 1 Blue

2 Violet

3 Violet

4 Violet-blue

5 Violet-blue

6 Fuchsia-red

7 Fuchsia-red

8 Dark blue

Example 1: Detection by ESI+M+=329 lambda max 578 nm

Example 2: Detection by ESI+M+=315 lambda max 556 nm

Example 3: Detection by ESI+M+=329 lambda max 564 nm

Example 4: Detection by ESI+M+=391 lambda max 576 nm

Example 5: Detection by ESI+M+=255 lambda max 569 nm

Example 6: Detection by ESI+M+=275 lambda max 528 nm

Example 7: Detection by ESI+M+=261 lambda max 534 nm

Example 8: Detection by ESI+M+=285 lambda max 572 nm

A coloration appears between 24 hours and 72 hours at room temperature.Formula of the Example Color isolated product  9 Violet-blue

10 Blue

11 Violet-blue

Example 9: lambda max 568 nm

Example 10: lambda max 630 nm

Example 11: lambda max 556 nm

The products isolated after reaction correspond to the compounds ofgeneral formula (I′).

B) Synthetic Process Using at Least One Hydrazone of Formula (A) and/or(B) and an Aldehyde of Formula R₂₃CHO

This synthetic process is performed in two steps:

1—A hydrazone of formula (A) or (B) is first reacted in the presence ofan aldehyde of formula R₂₃CHO, at least one polar solvent and an organicsalt. A compound of formula (A′) or (B′) represented below is formed andisolated:

The meanings of the radicals Z₁₄, Z₁₅, Z₁₆, Z₁₇, Z₁₈, Z₁₉, Z₂₀, R₂₃,R₂₅, R₂₆ and R₂₇ in the compounds of formula (A′) or (B′) are the sameas those in the compounds of formula (A) and (B).

Examples of Synthesis of Formulae A′ and B′

Syntheses Performed

The hydrazone 1 (1 9, 4.6 mmol) was placed in contact with4-pyridinecarboxaldehyde (0.7 ml, 7 mmol), 0.5 ml of acetic acid and 6ml of ethanol in a round-bottomed flask with stirring at 45° C. for 30minutes. After reaction, the reaction medium was concentrated todryness. The residue was taken up by adding 50 ml of ethyl acetate. Theprecipitate obtained was filtered off and then dried in a desiccator. 1g of a yellow powder was obtained.

Analysis:

MS(ES⁺): 213 (MH⁺) NMR (¹H, 400 MHz: 4.21 ppm (s, CH₃); 7.36 ppm (m,1H); 8.26 ppm (m, 2H) ; 8.37 ppm (m, 1H); 8.47 ppm (m, 2H); 8.80 ppm (s,1H); 8.91 ppm (m, 2H).

The following products were synthesized according to the same procedure:

Analysis:

Slightly colored powder

Yield: 98% MS(ES⁺): 212 (MH⁺) NMR (¹H, 400 MHz: 4.1 ppm (s, CH₃); 7.16ppm (m, 1H); 7.49 ppm (m, 2 Har); 7.81 ppm (m, 2 Har); 7.97 ppm (m, 1H);8.12 ppm (m, 1 Har); 8.35 ppm (m, 1H); 8.97 ppm (s, 1H).

Analysis:

Yellow powder

Yield: quantitative MS(ES⁺): 227 (M⁺) NMR (¹H, 400 MHz: 4.2 ppm (s,CH₃); 4.4 ppm (m, 1H); 7.37 ppm (m, 2H); 8.26 ppm (m, 2H); 8.44 ppm (m,2H); 8.75 ppm (s, 1H); 8.93 ppm (m, 2H)

2—The reaction is performed between pH 3 and pH 11 and preferablybetween pH 5 and pH 9.5 in aerobic medium at a temperature of between10° C. and 80° C. and preferably between 20° C. and 65° C. Theoxidoreductases used will be chosen from the following enzymes from thegroup EC 1.10.3, by way of example: catechol oxidase EC 1.10.3.1,laccase EC 1.10.3.2, L-ascorbate oxidase EC 1.10.3.3 and aminophenoloxidase EC 1.10.3.4.

The compound of formula (A′) or (B′) is the substrate for saidenzyme(s). A mediator may be introduced into the reaction mixture inorder to improve the reaction speed. Said mediator serves as anintermediate reagent between the enzyme and the compound of formula (A′)or (B′) or the compound of formula (A) or (B).

As examples of mediators that may be used, mention may be made of1-hydroxybenzotriazole, ABTS and TEMPO. The concentration of compound offormula (A) or (B) in the reaction medium is between 0.01 M and 3 M andpreferably between 0.1 M and 1 M. The concentration of compound offormula (A′) or (B′) in the reaction medium is between 0.01 M and 3 Mand preferably between 0.1 M and 1 M.

The reagents: the compound of formula (A) or (B) and the compound offormula (A′) or (B′), the enzyme(s) and/or the mediator for said enzyme,and/or the oxidizing agent are mixed together and the pH and temperatureare adjusted.

Example 12

0.3 M Laccase 1000 U N-hydroxyethylpyridone-2-hydrazone 0.3 M 30 mMbuffer qs 100 ml KH₂PO₄/K₂HPO₄ pH 7.5 Example Color Formula 12Violet-blue

C) Synthetic Process Using at Least One Hydrazone of Formula (A) and/or(B) and a Compound of Formula R″₂₃C(OR₂₄)₃

The hydrazone of formula (A) or (B) used for the synthesis is reacted inthe presence of one equivalent of a compound of formula R″₂₃C(OR₂₄)₃ andoptionally a protic solvent with a boiling point ranging between 66° C.and 180° C., at a temperature of between 30° C. and 150° C. withstirring. Preferably, the hydrazone of formula (A) or (B) is reacted inthe presence of trimethyl orthoformate or triethyl orthoacetate andoptionally a solvent, preferably chosen from methanol and ethanol, at atemperature of between 100° C. and 150° C., for a period of between 30and 60 minutes.

Depending on the nature of the hydrazone used, a compound of formulae(F1), (F2) or (G1), (G2) below may be obtained:

When the compounds of formula (F1) or (F2) are obtained, they may besubsequently converted into tetraazapentamethine compounds of formula(I) in the following manner:

The compound of formula (F1) or (F2) and a compound of formula (A) or(B) are reacted in the presence of an oxidizing agent in a polarsolvent, at a temperature of between 0° C. and 120° C. The pH of thesolution is between 3 and 11.5. The oxidizing agent is chosen from O₂,Na₂O, K₃Fe(CN)₆, MnO₂, H₂O₂, Ag₂O, AgO, NiO₂, NaBO₃, Na₂S₂O₈, CH₃CO₃H,C₆H₅CO₃H, (NH₄)₂Ce(NO₃)₆, PbO₂, Pb(OCOCH₃)₄, SeO₂ and CrO₃.2C₅H₄N. Thepreferred oxidizing agents will be chosen from K₃Fe(CN)₆, MnO₂, H₂O₂ andPb(OCOCH₃)₄. Preferably, the preferred oxidizing agents will be chosenfrom O₂, K₃Fe(CN)₆, MnO₂ and H₂O₂. The reaction is preferably performedat a temperature of between 0° C. and 80° C. in a solvent, preferably apolar solvent, at a pH of between 5 and 9.5.

Examples of Synthesis of Formulae G1 and G2

The hydrazone 1 (0.23 g, 1 mmol) was placed in contact with triethylorthoformate (0.15 ml, 1 mmol) in a round-bottomed flask with stirringat 130° C. for 30 minutes. After reaction, the reaction medium wasconcentrated to dryness. The residue was taken up by adding 10 ml ofdiisopropyl ether. The precipitate obtained was filtered off and thendried in a desiccator. 0.15 g of a white powder was obtained. Yield:41%.

Analysis:

White powder

NMR (¹H, 400 MHz): 3.63 ppm (s, 2CH₃); 7.2 ppm (m, 2H); 7.30 ppm (m, 2H); 7.43 ppm (m, 2 H); 7.59 ppm (m, 2H); 8.17 ppm (s, 1H).

Example 13

1^(st) Step:

The hydrazone 1 (4.28 g, 0.01998 mol) is placed in contact with triethylorthoformate (50 ml, 0.30 mol) in a round-bottomed flask with stirringat 130° C. for 12 hours. The reaction medium was cooled and the productwas precipitated from diisopropyl ether. The precipitate was filteredoff under vacuum and then stored under argon. Quantitative yield.

Analysis:

MS(ES⁺): 180 (MH⁺) NMR (¹H, 400 MHz): 1.38 ppm (t, CH₃); 3.93 ppm (m,CH₃); 4.30 ppm (t, CH₂); 6.97 ppm (m, Har); 7.64 ppm (m, Har); 8.15-7.97ppm (m, 2 Har); 8.36 ppm (s, CH).

2^(nd) Step:

Compound 2 (0.1 g, 0.558 mol), compound 1 (0.119 g, 0.558 mol) andpyridine (16.74 ml) were stirred in a round-bottomed flask. The mediumwas heterogeneous. Aqueous ammonia (0.84 ml, rapid addition) and aqueouspotassium hexacyanoferrate (III) solution (K₃Fe(CN)₆/H₂O: 0.81 g/5.94ml, rapid dropwise addition) were then successively added to thereaction medium. A violet and then dark blue coloration was obtainedafter stirring for 1.5 hours. The product was precipitated in thepresence of diisopropyl ether and ethyl acetate, and then filtered off.It was subsequently washed with ethyl acetate.

Analysis:

MS(ES⁺): 255 (M⁺) λmax: 589 nm ε=79800

Example 14

Step 1

2.42 g of the hydrazone (1) (0.01 mol) and 3.15 g of compound (2) (0.01mol) in 60 ml of ethanol are stirred in a beaker. 1 M sodium hydroxidesolution is added to pH 7.5. The reaction is stirred in the open air for72 hours. The reaction is monitored by TLC. Once the reaction iscomplete, 100 ml of acetone are added to the reaction medium, which isstirred for 30 minutes. A dark precipitate appears. This precipitate isfiltered off and then dried under vacuum. A dark blue powder isobtained.Step 2

0.5 g of compound 3 obtained in the preceding step is dissolved in 3 mlof DMF in a round-bottomed flask. 1 ml of dimethyl sulfate is thenadded. The reaction is stirred for 15 hours. The reaction medium changedcolor, changing from blue to fuchsia. The reaction medium is poured intodiisopropyl ether. The residue obtained is taken up in ethanol. Bysuccessive addition of ethyl acetate and acetone, a precipitate isobserved and then filtered off and finally dried in a desiccator. A darkfuchsia powder is obtained.

The synthesis presented above allowed the following compounds to beprepared: Example Color Formula 15 Blue

16 Violet

Application Example

The following dye composition was prepared: (amounts expressed as gramsof active material) Dye of Example 1 according to the invention 0.2Hydroxyethylcellulose 0.72 Nonionic surfactant: 3.00 (50/50 C8/C10)alkylpolyglucoside as an aqueous 60% solution Benzyl alcohol 4.00Polyethylene glycol (8 EO) 6.00 Preserving agents 0.06 Borate buffer qspH 9 50 Demineralized water 100

The composition was applied on the one hand to locks of natural grayhair containing 90% white hairs, and on the other hand to locks ofpermanent-waved gray hair containing 90% white hairs, for 30 minutes atroom temperature (20° C.).

After the leave-in time, the locks were rinsed, shampooed and thenrinsed and dried. They were dyed in a very chromatic violet-blue shade.

Example of Bleaching

a) Dyeing

An aqueous solution of dye of Example 1 according to the invention (at0.5% by weight) is applied to a lock of natural gray hair containing 90%white hairs (0.5 g), at pH 7 (0.1 M potassium phosphate buffer) and isleft to act on the hair for 30 minutes at room temperature (20° C.).

The lock is then rinsed, shampooed and then dried. It was dyed in a verychromatic violet-blue shade.

b) Bleaching

5 ml of aqueous sodium hydrosulfite (or sodium dithionite) solution at5% by weight buffered to pH 7 with potassium phosphate (0.1 M) isapplied to a 0.5 g lock of hair obtained from step a), and is left toact on the hair for 5 minutes at room temperature (20° C.).

The lock is then rinsed, shampooed and then dried.

The lock obtained is bleached.

A lock of gray hair, i.e. the initial color of the hair before thedyeing treatment (step a), is obtained.

1. A tetraazapentamethine compound of formula (I′)

wherein W′₁ represents a cationic heteroaromatic radical of formula(II′) or (III′):

W′₂ represents a heteroaromatic radical of formula (IV′) or (V′):

wherein: Z′₀ represents a radical CR′₂, a nitrogen atom or a radicalNR′₂₁, Z′₁ represents an oxygen atom or a radical NR′₉, Z′₂ represents anitrogen atom or a radical CR′₁₀, Z′₃ represents a nitrogen atom or aradical CR′₁, Z′₄ represents a nitrogen atom or a radical CR′₁₂, Z′₅represents a nitrogen atom or a radical CR′₁₃, Z′₆ represents a nitrogenatom or a radical CR′₁₄, Z′₇ represents an oxygen atom or a radicalNR′₁₅, Z′₈ represents a nitrogen atom or a radical CR′₁₆, Z′₉ representsa nitrogen atom or a radical CR′₁₇, Z′₁₀ represents a nitrogen atom or aradical CR′₁₈, Z′₁₁ represents a nitrogen atom or a radical CR′₁₉, Z′₁₂represents a nitrogen atom or a radical CR′₂₀, Z′₁₃ represents a radicalCR′₆, a nitrogen atom or a radical NR′₂₂, wherein each of the rings offormulae (II′), (III′), (IV′) and (V′) comprise not more than threenitrogen atoms and that two of the three nitrogen atoms may becontiguous, the bond a of the 5-membered cationic heteroaromatic radicalof formula (II′) being linked to the nitrogen atom N₁ of formula (I′),the bond b of the 6-membered cationic heteroaromatic radical of formula(III′) being linked to the nitrogen atom N₁ of formula (I′), the doublebond a′ of the 5-membered heteroaromatic radical of formula (IV′) beinglinked to the nitrogen atom N₂ of formula (I′), the double bond b′ ofthe 6-membered heteroaromatic radical of formula (V′) being linked tothe nitrogen atom N₂ of formula (I′), the bond b, linking the cationicheteroaromatic radical of formula (III′) to the nitrogen atom N₁ offormula (I′), being in an ortho or para position relative to thenitrogen atom bearing the radical R′₄ when Z′₅ represents a radicalCR′₁₃; the bond b being in an ortho position relative to the nitrogenatom bearing the radical R′₄ when Z′₅ represents a nitrogen atom, thebond b′, linking the heteroaromatic radical of formula (V′) to thenitrogen atom N₂ of formula (I′), being in an ortho or para positionrelative to the nitrogen atom bearing the radical R′₇ when Z′₁₁represents a radical CR′₁₉; the bond b′ being in an ortho positionrelative to the nitrogen atom bearing the radical R′₇ when Z′₁₁represents a nitrogen atom, R′₂, R′₆, R′₁₀ and R′₁₆ represent,independently of each other, a hydrogen atom; a linear or branched C₁-C₄alkyl radical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; a phenylradical, which is unsubstituted or substituted with one or two radicalschosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino andC₁-C₂ (di)alkylamino radicals; a carboxyl radical; a sulfonylaminoradical, R′₁, R′₄, R′₅, R′₇, R′₉, R′₁₅, R′₂₁ and R′₂₂ represent,independently of each other, a linear or branched C₁-C₈ alkyl radical,which is unsubstituted or substituted with one to three radicals chosenfrom hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂(di)alkylamino, carboxyl and sulfonic radicals; R′₀, R′₃, R′₈, R′₁₁,R′¹², R′₁₃ R′₁₄, R′₁₇, R′₁₈, R′₁₉ and R′₂₀ represent, independently ofeach other, a hydrogen atom, a linear or branched C₁-C₁₆hydrocarbon-based chain, this chain possibly being saturated orunsaturated with one to three unsaturations, this chain beingunsubstituted or substituted with one to three radicals chosen fromhydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂(di)alkylamino, carboxyl, sulfonic, sulfonylamino and C₂-C₄(poly)hydroxyalkylamino radicals or a halogen atom such as chlorine,fluorine or bromine; a phenyl radical, which is unsubstituted orsubstituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino,carboxyl, sulfonic, sulfonylamino and C₂-C₄ (poly)hydroxyalkylaminoradicals or a halogen atom such as chlorine, fluorine or bromine; aheteroaryl radical chosen from pyrazolyl, pyrrolyl, imidazolyl,thiazolyl, oxazolyl, triazolyl, pyridyl, pyrimidinyl, triazinyl,pyrazinyl and pyridazinyl radicals; in addition, this hydrocarbon-basedchain may be interrupted with one or two oxygen, nitrogen or sulfuratoms or with an SO₂ radical, R′₂ with R′₁₀, R′₁₁ with R′₁₂, R′₆ withR′₁₆, and R′₁₇ with R′₁₈ being able to form, independently of eachother, a 5- or 6-membered carbon-based aromatic ring, which isunsubstituted or substituted with one or two hydroxyl, amino,(di)(C₁-C₂)alkylamino, C₁-C₂ alkoxy or C₂-C₄ (poly)hydroxyalkylaminoradicals, subject to W′₁ and W′₂ not representing, simultaneously, thesame bicyclic system, wherein R′₀, R′₃, R′₈, R′₁₁, R′₁₂, R′₁₃, R′₁₄,R′₁₇, R′₁₈, R′₁₉ and R′₂₀ do not comprise a peroxide bond or diazo ornitroso radicals, X is an organic or mineral anion.
 2. The compound offormula (I′) as claimed in claim 1, wherein R′₀ represents a hydrogenatom; a linear or branched C₁-C₆ alkyl radical, which is unsubstitutedor substituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, C₂-C₄(poly)hydroxyalkylamino, carboxyl and sulfonic radicals; a phenylradical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals or a halogenatom such as chlorine, fluorine or bromine; an optionally cationicheteroaryl radical chosen from pyrazolyl, pyrrolyl, imidazolyl,thiazolyl, oxazolyl, triazolyl, pyridyl, pyrimidinyl, triazinyl,pyrazinyl and pyridazinyl radicals.
 3. The compound of formula (I′) asclaimed in claim 1 wherein R′₀ represents a hydrogen atom; a methyl,ethyl or 2-methoxyethyl radical; a phenyl radical, which isunsubstituted or substituted with an amino, (di)methylamino or(di)(2-hydroxyethyl)amino radical, or optionally a cationic heteroarylradical chosen from pyrazolyl, pyrrolyl, imidazolyl and pyridylradicals.
 4. The compound of formula (I′) as claimed in claim 1, whereinR′₂, R′₆, R′₁₀ and R′₁₆ represent a hydrogen atom, a C₁-C₄ alkylradical, which is unsubstituted or substituted with one or two radicalschosen from hydroxyl, amino, C₁-C₂ (di)alkylamino and carboxyl radicals,or a phenyl radical.
 5. The compound of formula (I′) as claimed in claim1 wherein R′₂, R′₆, R′₁₀ and R′₁₆ represent a hydrogen atom, a methyl,phenyl or 2-hydroxymethyl radical or a carboxyl.
 6. The compound offormula (I′) as claimed in claim 1, wherein R′₁, R′₄, R′₅, R′₇, R′₉,R′₁₅, R′₂₁ and R′₂₂ represent a C₁-C₄ alkyl radical, which isunsubstituted or substituted with one or two radicals chosen fromhydroxyl, C₁-C₂ alkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl andsulfonic radicals.
 7. The compound of formula (I′) as claimed in claim1, wherein R′₁, R′₄, R′₅, R′₇, R′₉, R′₁₅, R′₂₁ and R′₂₂ represent amethyl, ethyl, 2-hydroxyethyl, 1-carboxymethyl, 2-carboxyethyl or2-sulfonylethyl radical.
 8. The compound of formula (I′) as claimed inclaim 1, wherein R′₃, R′₈, R′₁₁, R′₁₂, R′₁₃, R′₁₄, R′₁₇, R′₁₈, R′₁₉ andR′₂₀ represent, independently of each other, a hydrogen atom; a linearor branched C₁-C₄ alkyl radical, which is unsubstituted or substitutedwith one or two radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonicradicals; a phenyl radical, which is unsubstituted or substituted withone or two radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino, C₁-C₂ (di) alkylamino, carboxyl and sulfonicradicals or a halogen atom such as chlorine, fluorine or bromine; asulfonylamino radical; a C₂-C₄ (poly)hydroxyalkylamino radical.
 9. Thecompound of formula (I′) as claimed in claim 1, wherein R′₃, R′₈, R′₁₁,R′₁₂, R′₁₃, R′₁₄, R′₁₇, R′₁₈, R′₁₉ and R′₂₀ represent, independently ofeach other, a hydrogen atom, a methyl or 2-hydroxymethyl radical, acarboxyl, a methoxy, ethoxy or 2-hydroxyethyloxy radical, or an amino,methylamino, dimethylamino or 2-hydroxyethylamino radical.
 10. Thecompound of formula (I′) as claimed in claim 1, wherein W′₁ is a2-pyridinium radical and W′₂ is a 2-pyridine radical, selected from thegroup consisting of:2-[5-(N-methyl-2-pyridinylidene)-1-formazano]-N-methylpyridiniumchloride2-[5-(N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-N-methylpyridiniumchloride2-[5-(N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-N-methylpyridiniumchloride2-[5-(N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-N-methylpyridiniumchloride2-[5-(N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-N-methylpyridiniumchloride2-[S-(N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-methylpyridiniumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-methylpyridiniumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(4-pyrrolidino-N-methyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-4-pyrrolidino-N-methylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-1-formazano]-N-hydroxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-N-hydroxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-N-hydroxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-phenyl-1-formazano)-N-hydroxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-N-hydroxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-hydroxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-hydroxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-hydroxyethylpyridiniumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-1-formazano]-N-carboxyethylpyridiniumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(2-pyridinyl)-1-formazano]-N-hydroxyethylpyridiniumbromide 2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(2-N-methylpyridinyliummethosulfate)-1-formazano]-N-hydroxyethylpyridinium bromide2-[5-(N-carboxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-N-carboxyethylpyridiniumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-N-carboxyethylpyridiniumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-N-carboxyethylpyridiniumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-N-carboxyethylpyridiniumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-carboxyethylpyridiniumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-carboxyethylpyridiniumchloride and2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-carboxyethylpyridiniumchloride
 11. The compound of formula (I′) as claimed in claim 1, whereinW′₁ is a 4-pyridinium radical and W′₂ is a 4-pyridine radical, selectedfrom the group consisting of:4-[5-(N-methyl-4-pyridinylidene)-1-formazano]-N-methylpyridiniumchloride4-[5-(N-methyl-4-pyridinylidene)-3-methyl-1-formazano]-N-methylpyridiniumchloride4-[5-(N-methyl-4-pyridinylidene)-3-ethyl-1-formazano]-N-methylpyridiniumchloride4-[5-(N-methyl-4-pyridinylidene)-3-isopropyl-1-formazano]-N-methylpyridiniumchloride4-[5-(N-methyl-4-pyridinylidene)-3-phenyl-1-formazano]-N-methylpyridiniumchloride4-[5-(N-methyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-methylpyridiniumchloride4-[5-(N-methyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-methylpyridiniumchloride4-[5-(N-methyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-methylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-hydroxyethylpyridiniumchloride4-[5-(N-carboxyethyl-4-pyridinylidene)-1-formazano]-N-carboxyethylpyridiniumchloride4-[5-(N-carboxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-N-carboxyethylpyridiniumchloride4-[5-(N-carboxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-N-carboxyethylpyridiniumchloride4-[5-(N-carboxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-N-carboxyethylpyridiniumchloride4-[5-(N-carboxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-N-carboxyethylpyridiniumchloride4-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-N-carboxyethylpyridiniumchloride4-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-N-carboxyethylpyridiniumchloride and4-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-N-carboxyethylpyridiniumchloride.
 12. The compound of formula (I′) as claimed in claim 1,wherein W′₁ is a 2-imidazolium radical and W′₂ is a 2-imidazole radical,selected from the group consisting of:2-[5-(1,3-dimethyl-2-imidazolidene)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dimethyl-2-imidazolidene)-3-methyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dimethyl-2-imidazolidene)-3-ethyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dimethyl-2-imidazolidene)-3-isopropyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dimethyl-2-imidazolidene)-3-phenyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dimethyl-2-imidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dimethyl-2-imidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dimethyl-2-imidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-methyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-imidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-methyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride and2-[5-(1,3-dicarboxyethyl-2-imidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride
 13. The compound of formula (I′) as claimed in claim 1, whereinW′₁ is a 5-pyrazolium radical and W′₂ is a 5-pyrazole radical, selectedfrom the group consisting of:5-[5-(1,2-dimethyl-5-pyrazolidene)-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dimethyl-5-pyrazolidene)-3-methyl-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dimethyl-5-pyrazolidene)-3-ethyl-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dimethyl-5-pyrazolidene)-3-isopropyl-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dimethyl-5-pyrazolidene)-3-phenyl-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dimethyl-5-pyrazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dimethyl-5-pyrazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dimethyl-5-pyrazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,2-dimethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-methyl-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-ethyl-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-phenyl-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-isopropyl-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dihydroxyethyl-5-pyrazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,2-dihydroxyethylpyrazoliniumchloride5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-methyl-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-ethyl-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-phenyl-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-isopropyl-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride and5-[5-(1,2-dicarboxyethyl-5-pyrazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,2-dicarboxyethylpyrazoliniumchloride
 14. The compound of formula (I′) as claimed in claim 1, whereinW′₁ is a 2-benzimidazolium radical and W′₂ is a 2-pyridine radical,selected from the group of consisting of:2-[5-(N-methyl-2-pyridinylidene)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride and2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride
 15. The compound of formula (I′) as claimed in claim 1, whereinW′₁ is a 2-benzimidazolium radical and W′₂ is a 4-pyridine radical,selected from the group consisting of:2-[5-(N-methyl-4-pyridinylidene)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride and2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride
 16. The compound of formula (I′) as claimed in claim 1, whereinW′₁ is a 2-imidazolium radical and W′₂ is a 2-pyridine radical, selectedfrom the group consisting of:2-[5-(N-methyl-2-pyridinylidene)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride and2-[5-(N-carboxyethyl-2-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride
 17. The compound of formula (I′) as claimed in claim 1, whereinW′₁ is a 2-imidazolium radical and W′₂ is a 4-pyridine radical, selectedfrom the group consisting of:2-[5-(N-methyl-4-pyridinylidene)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-methyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dimethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-hydroxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-methyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride and2-[5-(N-carboxyethyl-4-pyridinylidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylimidazoliumchloride
 18. A process for preparing the compound of formula (I′) asclaimed in claim 1, wherein at least two equivalents of at least onehydrazone chosen from the hydrazones of formula A and the hydrazones offormula B:

wherein Z₁₄, Z₁₅, Z₁₆ and R₂₅ have the same meanings as Z′₇, Z′₈, Z′₁₃,and R′₅, respectively, of formula (IV′), Y being an organic or mineralanion, [[X]] x being an integer ranging from 1 to 3, Z₁₇, Z₁₈, Z₁₉, Z₂₀,R₂₆ and R₂₇, have the same meanings as Z′₉, Z′₁₀, Z′₁₁, Z′₁₂, R′₈ andR′₇, respectively, of formula (V′), Y′ being an organic or mineralanion, and x′ being an integer ranging from 1 to 3, are reacted with oneequivalent of an aldehyde of formula R₂₃CHO, wherein R₂₃ has the samemeaning as R′₀ of formula (I′).
 19. The preparation process as claimedin claim 18, wherein the aldehyde of formula R₂₃CHO is obtained from analdehyde precursor of formula R′₂₃CH₂OH in the presence of an oxidizingsystem, wherein R′₂₃ has the same meaning as R′₀ of formula (I′) definedin claim
 1. 20. A method of dyeing keratin fibers with at least onetetraazapentamethine compound of formula (I) comprising applying saidcompound to the keratin fibers, wherein

wherein W₁ represents a cationic heteroaromatic radical of formula (II)or (III)

W₂ represents a hetero aromatic radical of formula (IV) or (V)

wherein: Z₀ represents a radical CR₂, a nitrogen atom or a radical NR₂₁,Z₁ represents an oxygen or sulfur atom or a radical NR₉, Z₂ represents anitrogen atom or a radical CR₁₀, Z₃ represents a nitrogen atom or aradical CR₁₁, Z₄ represents a nitrogen atom or a radical CR₁₂, Z₅represents a nitrogen atom or a radical CR₁₃, Z₆ represents a nitrogenatom or a radical CR₁₄, Z₇ represents an oxygen or sulfur atom or aradical NR₁₅, Z₈ represents a nitrogen atom or a radical CR₁₆, Z₉represents a nitrogen atom or a radical CR₁₇, Z₁₀ represents a nitrogenatom or a radical CR₁₈, Z₁₁ represents a nitrogen atom or a radicalCR₁₉, Z₁₂ represents a nitrogen atom or a radical R₂₀, Z₁₃ represents aradical CR₆ a nitrogen atom or a radical NR₂₂, wherein each of the ringsof formulae (II), (III), (IV) and (V) comprise not more than threenitrogen atoms and that two of the three nitrogen atoms may becontiguous, the bond a of the 5-membered cationic heteroaromatic radicalof formula (II) being linked to the nitrogen atom N₁ of formula (I), thebond b of the 6-membered cationic heteroaromatic radical of formula(III) being linked to the nitrogen atom N₁ of formula (I), the doublebond a′ of the 5-membered heteroaromatic radical of formula (IV) beinglinked to the nitrogen atom N₂ of formula (I), the double bond b′ of the6-membered heteroaromatic radical of formula (V) being linked to thenitrogen atom N₂ of formula (I), the bond b, linking the cationicheteroaromatic radical of formula (III) to the nitrogen atom N₁ offormula (I), being in an ortho or para position relative to the nitrogenatom bearing the radical R₄ when Z₅ represents a radical CR₁₃; the bondb being in an ortho position relative to the nitrogen atom bearing theradical R₄ when Z₅ represents a nitrogen atom, the bond b′, linking theheteroaromatic radical of formula (V) to the nitrogen atom N₂ of formula(I), being in an ortho or para position relative to the nitrogen atombearing the radical R₇ when Z₁₁ represents a radical CR₁₉; the bond b′being in an ortho position relative to the nitrogen atom bearing theradical R₇ when Z₁₁ represents a nitrogen atom, R₂, R₆, R₁₀ and R₁₆represent, independently of each other, a hydrogen atom; a linear orbranched C₁-C₄ alkyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonicradicals; a phenyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino and C₁-C₂ (di)alkylamino radicals; a carboxylradical; a sulfonylamino radical, R₁, R₄, R₅, R₇, R₉, R₁₅, R₁₂ and R₂₂represent, independently of each other, a linear or branched C₁-C₈ alkylradical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; R₀, R₃, R₈,R₁₁, R₁₂, R₁₃, R₁₄, R₁₇, R₁₈, R₁₉ and R₂₀ represent, independently ofeach other, a hydrogen atom, a linear or branched C₁-C₁₆hydrocarbon-based chain, this chain possibly being saturated orunsaturated with one to three unsaturations, this chain beingunsubstituted or substituted with one to three radicals chosen fromhydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂(di)alkylamino, carboxyl, sulfonic, sulfonylamino and C₂-C₄(poly)hydroxyalkylamino radicals or a halogen atom such as chlorine,fluorine or bromine; a phenyl radical, which is unsubstituted orsubstituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino,carboxyl, sulfonic, sulfonylamino and C₂-C₄ (poly)hydroxyalkylaminoradicals or a halogen atom such as chlorine, fluorine or bromine; aheteroaryl radical chosen from pyrazolyl, pyrrolyl, imidazolyl,thiazolyl, oxazolyl, triazolyl, pyridyl, pyrimidinyl, triazinyl,pyrazinyl and pyridazinyl radicals; in addition, this hydrocarbon-basedchain may be interrupted with one or two oxygen, nitrogen or sulfuratoms or with an SO₂ radical, wherein R₀, R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄,R₁₇, R₁₈, R₁₉ and R₂₀ do not comprise a peroxide bond or diazo ornitroso radicals, R₂ with R₁₀, R₁₁ with R₁₂, R₆ with R₁₆, and R₁₇ withR₁₈ can form, independently of each other, a 5- or 6-memberedcarbon-based aromatic ring, which is unsubstituted or substituted withone or two hydroxyl, amino, (di)(C₁-C₂)alkylamino, C₁-C₂ alkoxy or C₂-C₄(poly)hydroxyalkylamino radicals, X is an organic or mineral anion. 21.A process for preparing a tetraazapentamethine compound of formula (I)

wherein W₁ represents a cationic heteroaromatic radical of formula (II)or (III)

W₂ represents a heteroaromatic radical of formula (IV) or (V)

wherein: Z₀ represents a radical CR₂, a nitrogen atom or a radical NR₂₁,Z₁ represents an oxygen or sulfur atom or a radical NR₉, Z₂ represents anitrogen atom or a radical CR₁₀, Z₃ represents a nitrogen atom or aradical CR₁₁, Z₄ represents a nitrogen atom or a radical CR₁₂, Z₅represents a nitrogen atom or a radical CR₁₃, Z₆ represents a nitrogenatom or a radical CR₁₄, Z₇ represents an oxygen or sulfur atom or aradical NR₁₅, Z₈ represents a nitrogen atom or a radical CR₁₆, Z₉represents a nitrogen atom or a radical CR₁₇, Z₁₀ represents a nitrogenatom or a radical CR₁₈, Z₁₁ represents a nitrogen atom or a radicalCR₁₉, Z₁₂ represents a nitrogen atom or a radical CR₂₀, Z₁₃ represents aradical CR₆, a nitrogen atom or a radical NR₂₂, wherein each of therings of formulae (II), (III), (IV) and (V) comprise not more than threenitrogen atoms and that two of the three nitrogen atoms may becontiguous, the bond a of the 5-membered cationic heteroaromatic radicalof formula (II) being linked to the nitrogen atom N₁ of formula (I), thebond b of the 6-membered cationic heteroaromatic radical of formula(III) being linked to the nitrogen atom N₁ of formula (I), the doublebond a′ of the 5-membered heteroaromatic radical of formula (IV) beinglinked to the nitrogen atom N₂ of formula (I), the double bond b′ of the6-membered heteroaromatic radical of formula (V) being linked to thenitrogen atom N₂ of formula (I), the bond b, linking the cationicheteroaromatic radical of formula (III) to the nitrogen atom N₁ offormula (I), being in an ortho or para position relative to the nitrogenatom bearing the radical R₄ when Z₅ represents a radical CR₁₃; the bondb being in an ortho position relative to the nitrogen atom bearing theradical R₄ when Z₅ represents a nitrogen atom, the bond b′, linking theheteroaromatic radical of formula (V) to the nitrogen atom N₂ of formula(I), being in an ortho or para position relative to the nitrogen atombearing the radical R₇ when Z₁₁ represents a radical CR₁₉; the bond b′being in an ortho position relative to the nitrogen atom bearing theradical R₇ when Z₁₁ represents a nitrogen atom, R₂, R₆, R₁₀ and R₁₆represent, independently of each other, a hydrogen atom; a linear orbranched C₁-C₄ alkyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₁-C₄(poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonicradicals; a phenyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₁-C₄(poly)hydroxyalkoxy, amino and C₁-C₂ (di)alkylamino radicals; a carboxylradical; a sulfonylamino radical, R₁, R₄, R₅, R₇, R₉, R₁₅, R₂₁ and R₂₂represent, independently of each other, a linear or branched C₁-C₈ alkylradical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; R₀, R₃, R₈,R₁₁, R₁₂, R₁₃, R₁₄, R₁₇, R₁₈, R₁₉, and R₂₀ represent, independently ofeach other, a hydrogen atom, a linear or branched C₁-C₁₆hydrocarbon-based chain, this chain possibly being saturated orunsaturated with one to three unsaturations, this chain beingunsubstituted or substituted with one to three radicals chosen fromhydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂(di)alkylamino, carboxyl, sulfonic, sulfonylamino and C₂-C₄(poly)hydroxyalkylamino radicals or a halogen atom such as chlorine,fluorine or bromine; a phenyl radical, which is unsubstituted orsubstituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino,carboxyl, sulfonic, sulfonylamino and C₂-C₄ (poly)hydroxyalkylaminoradicals or a halogen atom such as chlorine, fluorine or bromine; aheteroaryl radical chosen from pyrazolyl, pyrrolyl, imidazolyl,thiazolyl, oxazolyl, triazolyl, pyridyl, pyrimidinyl, triazinyl,pyrazinyl and pyridazinyl radicals; in addition, this hydrocarbon-basedchain may be interrupted with one or two oxygen, nitrogen or sulfuratoms or with an SO₂ radical, wherein R₀, R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄,R₁₇, R₁₈, R₁₉ and R₂₀ do not comrise a peroxide bond or diazo or nitrosoradicals, R₂ with R₁₀, R₁₁, with R₁₂, R₆ with R₁₆ with R₁₈ can form,independently of each other, a 5- or 6-membered carbon-based aromaticring, which is unsubstituted or substituted with one or two hydroxyl,amino, (di)(C₁-C₂)alkylamino, C₁-C₂ alkoxy or C₁-C₄(poly)hydroxyalkylamino radicals, X is an organic or mineral anionwherein at least two equivalents of at least one hydrazone chosen fromthe hydrazones of formula A and the hydrazones of formula B:

wherein Z₁₄, Z₁₅, Z₁₆ and R₂₅ have the same meanings as Z₇, Z₈, Z₁₃, andR₅, respectively, of formula (IV), Y being an organic or mineral anion,x being an integer ranging from 1 to 3, Z₁₇, Z₁₈, Z₁₉, Z₂₀, R₂₆ and R₂₇have the same meanings as Z₉, Z₁₀, Z₁₁, Z₁₂, R₈ and R₇, respectively, offormula (V), Y′ being an organic or mineral anion, and x′ being aninteger ranging from 1 to 3, are reacted with one equivalent of analdehyde precursor of formula R′₂₃CH₂OH, wherein R′₂₃ has the samemeaning as R₀ of formula (I), and of at least one enzyme capable ofgenerating an aldehyde from the aldehyde precursor of formula R′₂₃CH₂OH.22. A composition for dyeing keratin fibers comprising, in a medium thatis suitable for dyeing, at least one compound of formula (I)

wherein W₁ represents a cationic heteroaromatic radical of formula (II)or (III)

W₂ represents a heteroaromatic radical of formula (IV) or (V)

wherein: Z₀ represents a radical CR₂, a nitrogen atom or a radical NR₂₁,Z₁ represents an oxygen or sulfur atom or a radical NR₉, Z₂ represents anitrogen atom or a radical CR₁₀, Z₃ represents a nitrogen atom or aradical CR₁₁, Z₄ represents a nitrogen atom or a radical CR₁₂, Z₅represents a nitrogen atom or a radical CR₁₃, Z₆ represents a nitrogenatom or a radical CR₁₄, Z₇ represents an oxygen or sulfur atom or aradical NR₁₅, Z₈ represents a nitrogen atom or a radical CR₁₆, Z₉represents a nitrogen atom or a radical CR₁₇, Z₁₀ represents a nitrogenatom or a radical CR₁₈, Z₁₁ represents a nitrogen atom or a radicalCR₁₉, Z₁₂ represents a nitrogen atom or a radical CR₂₀, Z₁₃ represents aradical CR₆, a nitrogen atom or a radical NR₂₂, wherein each of therings of formulae (II), (III), (IV) and (V) comprise not more than threenitrogen atoms and that two of the three nitrogen atoms may becontiguous, the bond a of the 5-membered cationic heteroaromatic radicalof formula (II) being linked to the nitrogen atom N₁ of formula (I), thebond b of the 6-membered cationic heteroaromatic radical of formula(III) being linked to the nitrogen atom N₁ of formula (I), the doublebond a′ of the 5-membered heteroaromatic radical of formula (IV) beinglinked to the nitrogen atom N₂ of formula (I), the double bond b′ of the6-membered heteroaromatic radical of formula (V) being linked to thenitrogen atom N₂ of formula (I), the bond b, linking the cationicheteroaromatic radical of formula (III) to the nitrogen atom N₁ offormula (I), being in an ortho or para position relative to the nitrogenatom bearing the radical R₄ when Z₅ represents a radical CR₁₃; the bondb being in an ortho position relative to the nitrogen atom bearing theradical R₄ when Z₅ represents a nitrogen atom, the bond b′, linking theheteroaromatic radical of formula (V) to the nitrogen atom N₂ of formula(I), being in an ortho or para position relative to the nitrogen atombearing the radical R₇ when Z₁₁ represents a radical CR₁₉; the bond b′being in an ortho position relative to the nitrogen atom bearing theradical R₇ when Z₁₁ represents a nitrogen atom, R₂, R₆, and R₁₆represent, independently of each other, a hydrogen atom; a linear orbranched C₁-C₄ alkyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonicradicals; a phenyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino and C₁-C₂ (di)alkylamino radicals; a carboxylradical; a sulfonylamino radical, R₁, R₄, R₅, R₇, R₉, R₂₁ and R₂₂represent, independently of each other, a linear or branched C₁-C₈ alkylradical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₁-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; R₀, R₃, R₈,R₁₁, R₁₂, R₁₃, R₁₄, R₁₇, R₁₈, R₁₉ and R₂₀ represent, independently ofeach other, a hydrogen atom, a linear or branched C₁-C₁₆hydrocarbon-based chain, this chain possibly being saturated orunsaturated with one to three unsaturations, this chain beingunsubstituted or substituted with one to three radicals chosen fromhydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂(di)alkylamino, carboxyl, sulfonic, sulfonylamino and C₂-C₄(poly)hydroxyalkylamino radicals or a halogen atom such as chlorine,fluorine or bromine; a phenyl radical, which is unsubstituted orsubstituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino,carboxyl, sulfonic, sulfonylamino and C₂-C₄ (poly)hydroxyalkylaminoradicals or a halogen atom such as chlorine, fluorine or bromine; aheteroaryl radical chosen from pyrazolyl, pyrrolyl, imidazolyl,thiazolyl, oxazolyl, triazolyl, pyridyl, pyrimidinyl, triazinyl,pyrazinyl and pyridazinyl radicals; in addition, this hydrocarbon-basedchain may be interrupted with one or two oxygen, nitrogen or sulfuratoms or with an SO₂ radical, wherein R₀, R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄,R₁₇, R₁₈, R₁₉ and R₂₀ do not comprise a peroxide bond or diazo ornitroso radicals, R₂, with R₁₀, R₁₁ with R₁₂, R₆ with R₁₆, and R₁₇ withR₁₈ can form, independently of each other, a 5- or 6-memberedcarbon-based aromatic ring, which is unsubstituted or substituted withone or two hydroxyl, amino, (di)(C₁-C₂)alkylamino, C₁-C₂ alkoxy or C₂-C₄(poly)hydroxyalkylamino radicals, X is an organic or mineral anion or offormula (I′) as claimed in claim 1, as a direct dye.
 23. The compositionas claimed in claim 22, wherein, in formula (I), W₁ is a2-benzimidazolium radical and W₂ is a 2-benzimidazole radical.
 24. Thecomposition as claimed in claim 23, wherein the compounds of formula (I)are selected from the group consisting of:2-[5-(1,3-dimethyl-2-benzimidazolidene)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-methyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-ethyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-isopropyl-1-formazano]-1,3-dimethylbenzimidazolium2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-phenyl-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-(4′methoxyphenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dimethylbenzimidazoliumchloride 2-[5-(1,3-dimethyl-2-benzimidazolidene)-3-(4′-N₁N-dimethylaminophenyl)-1-formazano]-1,3-dimethylbenzimidazolium chloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-methyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-ethyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-phenyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-isopropyl-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dihydroxyethyl-2-benzimidazolidene)-3-(4′-N,N-dimethylaminophenyl)-1-formazano]-1,3-dihydroxyethylbenzimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-methyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-ethyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-phenyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-isopropyl-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-(4′-methoxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-(4′-hydroxyphenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride and 2-[5-(1,3-dicarboxyethyl-2-benzimidazolidene)-3-(4′-N₁N-dimethylaminophenyl)-1-formazano]-1,3-dicarboxyethylbenzimidazoliumchloride
 25. The composition as claimed in claim 22, wherein thecompound(s) of formula (I) is (are) present in a concentration rangingfrom 0.001% to 5% by weight relative to the total weight of thecomposition.
 26. The composition as claimed in claim 22, wherein saidcomposition further comprises at least one oxidation base selected fromthe group consisting of para-phenylenediamines,bis(phenyl)alkylenediamines, para-aminophenols, ortho-aminophenols andheterocyclic bases, the addition salts thereof, and mixtures thereof.27. The composition as claimed in claim 26, wherein the oxidationbase(s) is (are) present in a concentration ranging from 0.001% to 10%by weight relative to the total weight of the composition.
 28. Thecomposition as claimed in claim 22, wherein said composition furthercomprises at least one coupler selected from the group consisting ofmeta-phenylenediamines, meta-aminophenols, meta-diphenols,naphthalene-based couplers and heterocyclic couplers, the addition saltsthereof, and mixtures thereof.
 29. The composition as claimed in claim28, the coupler(s) is (are) present in a concentration ranging from0.001% to 10% by weight relative to the total weight of the composition.30. The composition as claimed in claim 22, wherein said compositioncomprises at least one direct dye other than the compounds of formula(I).
 31. The composition as claimed in claim 30, wherein the additionaldirect dye(s) is (are) present in a concentration ranging from 0.001% to20% by weight relative to the total weight of the composition.
 32. Thecomposition as claimed in claim 22, wherein said composition furthercomprises an oxidizing agent.
 33. A process for dyeing keratin fibers,wherein at least one composition as claimed in claim 22 is applied tosaid fibers, for a time that is sufficient to develop the desiredcoloration.
 34. The process as claimed in claim 33, wherein the dyecomposition further comprises an oxidizing agent.
 35. The process asclaimed in claim 34, wherein the oxidizing agent is mixed at the time ofuse with the dye composition.
 36. The process as claimed in claim 34,wherein the oxidizing agent is applied to the fibers simultaneously withor sequentially to the dye composition.
 37. A process for the oxidationdyeing of keratin fibers, wherein at least one dye composition asdefined in claim 22 further comprising at least one oxidation base andoptionally at least one coupler, in the presence of an oxidizing agent,is applied to the fibers.
 38. The process as claimed in claim 37,wherein the oxidizing agent is mixed at the time of use with the dyecomposition.
 39. The process as claimed in claim 37, wherein theoxidizing agent is applied to the fibers simultaneously with orsequentially to the dye composition.
 40. A process for bleaching acompound of formula (I)

wherein W₁ represents a cationic heteroaromatic radical of formula (II)or (III)

W₂ represents a heteroaromatic radical of formula (IV) or (V)

wherein: Z₀ represents a radical CR₂, a nitrogen atom or a radical NR₂₁,Z₁ represents an oxygen or sulfur atom or a radical NR₉. Z₂ represents anitrogen atom or a radical CR₁₀, Z₃ represents a nitrogen atom or aradical CR₁₁, Z₄ represents a nitrogen atom or a radical CR₁₂, Z₅represents a nitrogen atom or a radical CR₁₃, Z₆ represents a nitrogenatom or a radical CR₁₄, Z₇ represents an oxygen or sulfur atom or aradical NR₁₅, Z₈ represents a nitrogen atom or a radical CR₁₆, Z₉represents a nitrogen atom or a radical CR₁₇, Z₁₀ represents a nitrogenatom or a radical CR₁₈, Z₁₁ represents a nitrogen atom or a radicalCR₁₉, Z₁₂ represents a nitrogen atom or a radical CR₂₀, Z₁₃ represents aradical CR₆, a nitrogen atom or a radical NR₂₂, wherein each of therings of formulae (II), (III), (IV) and (V) comprise not more than threenitrogen atoms and that two of the three nitrogen atoms may becontiguous, the bond a of the 5-membered cationic heteroaromatic radicalof formula (II) being linked to the nitrogen atom N₁ of formula (I), thebond b of the 6-membered cationic heteroaromatic radical of formula(III) being linked to the nitrogen atom N₁ of formula (I), the doublebond a′ of the 5-membered heteroaromatic radical of formula (IV) beinglinked to the nitrogen atom N₂ of formula (I), the double bond b′ of the6-membered heteroaromatic radical of formula (V) being linked to thenitrogen atom N₂ of formula (I), the bond b, linking the cationicheteroaromatic radical of formula (III) to the nitrogen atom N₁ offormula (I′) being in an ortho or para position relative to the nitrogenatom bearing the radical R₄ when Z₅ represents a radical CR₁₃; the bondb being in an ortho position relative to the nitrogen atom bearing theradical R₄ when Z₅ represents a nitrogen atom, the bond b′, linking theheteroaromatic radical of formula (V) to the nitrogen atom N₂ of formula(I), being in an ortho or para position relative to the nitrogen atombearing the radical R₇ when Z₁₁ represents a radical CR₁₉; the bond b′being in an ortho position relative to the nitrogen atom bearing theradical R₇ when Z₁₁ represents a nitrogen atom, R₂, R₆, R₁₀ and R₁₆represent, independently of each other, a hydrogen atom; a linear orbranched C₁-C₄ alkyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonicradicals; a phenyl radical, which is unsubstituted or substituted withone to three radicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄(poly)hydroxyalkoxy, amino and C₁-C₂ (di)alkylamino radicals; a carboxylradical; a sulfonylamino radical, R₁, R₄, R₅, R₇, R₉, R₁₅, R₂₁ and R₂₂represent, independently of each other, a linear or branched C₁-C₈ alkylradical, which is unsubstituted or substituted with one to threeradicals chosen from hydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy,amino, C₁-C₂ (di)alkylamino, carboxyl and sulfonic radicals; R₀, R₃, R₈,R₁₁, R₁₂, R₁₃, R₁₄, R₁₇, R₁₈, R₁₉ and R₂₀ represent, independently ofeach other, a hydrogen atom, a linear or branched C₁-C₁₆hydrocarbon-based chain, this chain possibly being saturated orunsaturated with one to three unsaturations, this chain beingunsubstituted or substituted with one to three radicals chosen fromhydroxyl, C₁-C₂ alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂(di)alkylamino, carboxyl, sulfonic, sulfonylamino and C₂-C₄(poly)hydroxyalkylamino radicals or a halogen atom such as chlorine,fluorine or bromine; a phenyl radical, which is unsubstituted orsubstituted with one to three radicals chosen from hydroxyl, C₁-C₂alkoxy, C₂-C₄ (poly)hydroxyalkoxy, amino, C₁-C₂ (di)alkylamino,carboxyl, sulfonic, sulfonylamino and C₂-C₄ (poly)hydroxyalkylaminoradicals or a halogen atom such as chlorine, fluorine or bromine; aheteroaryl radical chosen from pyrazolyl, pyrrolyl imidazolyl,thiazolyl, oxazolyl, triazolyl, pyridyl, pyrimidinyl, triazinyl,pyirazinyl and pyridazinyl radicals; in addition, this hydrocarbon-basedchain may be interrupted with one or two oxygen, nitrogen or sulfuratoms or with an SO₂ radical, wherein R₀, R₃, R₈, R₁₁, R₁₂, R₁₃, R₁₄,R₁₇, R₁₈, R₁₉ and R₂₀ do not comprise a peroxide bond or diazo ornitroso radicals, R₂ with R₁₀ , R₁₁ with R₁₂, R₆ with R₁₆, with R₁₇ withR₁₈ can form, independently of each other, a 5- or 6-memberedcarbon-based aromatic ring, which is unsubstituted or substituted withone or two hydroxyl, amino, (di)(C₁-C₂)alkylamino, C₁-C₂ alkoxy or C₂-C₄(poly)hydroxyalkylamino radicals, X is an organic or mineral anion or acompound (I′) as claimed in claim 1, wherein a bleaching compositioncomprising at least one reducing agent chosen from reducing agentscomprising sulfur is applied to the compound of formula (I) or (I′). 41.A process for bleaching dyed keratin fibers, comprising a) applying ableaching composition comprising, in a suitable medium, at least onereducing agent chosen from sulfur-containing reducing agents to saidfibers dyed with a dye composition as defined in claim 22, b) leavingsaid composition to act for a time that is sufficient to obtainbleaching, c) optionally rinsing the fibers, and d) washing, rinsing anddrying the fibers.
 42. The process as claimed in claim 40 wherein thesulfur-containing reducing agents are selected from the compounds havinga thiol, sulfide or sulfite function.
 43. The process as claimed inclaim 42, wherein the thiols are selected from the group consisting ofthioglycolic acid, thiolactic acid, the alkali metal or alkaline-earthmetal salts thereof and esters thereof; β-mercaptoethanol; cystein,cysteamine and derivatives thereof; homocystein and a salt thereof;mercaptoaldehydes; penicillamine; glutathione; and mixtures thereof. 44.The process as claimed in claim 42, wherein the sulfites are selectedfrom the group consisting of alkali metal, alkaline-earth metal orammonium sulfates, metabisulfites or hydrosulfites, and mixturesthereof.
 45. The process as claimed in claim 40, wherein the reducingagent comprises sodium sulfite and sodium metabisulfite.
 46. The processas claimed in claim 42, wherein sulfides are are selected from the groupconsisting of sulfides and disulfides.
 47. The process as claimed inclaim 40, wherein the content of reducing agent in the composition isbetween 0.01% and 10% by weight of the bleaching composition.
 48. Theprocess as claimed in claim 35, wherein the oxidizing agent is appliedto the fibers simultaneously with or sequentially to the dyecomposition.
 49. The process as claimed in claim 41, wherein thesulfur-containing reducing agents are selected from compounds having athiol, sulfide or sulfite function.
 50. The process as claimed in claim49, wherein the thiols are selected from the group consisting ofthioglycolic acid, thiolactic acid, the alkali metal or alkaline-earthmetal salts thereof and esters thereof; β-mercaptoethanol; cystein,cysteamine and derivatives thereof; homocystein and a salt thereof;mercaptoaldehydes; penicillamine; glutathione; and mixtures thereof. 51.The process as claimed in claim 49, wherein the sulfites are selectedfrom the group consisting of alkali metal, alkaline-earth metal orammonium sulfates, metabisulfites or hydrosulfites, and mixturesthereof.
 52. The process as claimed in claim 41, wherein the reducingagent comprises sodium sulfite and sodium metabisulfite.
 53. The processas claimed in claim 49, wherein the sulfides are selected from the groupconsisting of sulfides and disulfides.
 54. The process as claimed inclaim 40, wherein the content of reducing agent in the composition isbetween 0.01% and 10% by weight of the bleaching composition.